Release v1.6.0 (#324)

* Update version and changelog for v1.6.0
* Update docs
diff --git a/docs/dyn/gmail_v1.users.threads.html b/docs/dyn/gmail_v1.users.threads.html
index 334231c..245e9ab 100644
--- a/docs/dyn/gmail_v1.users.threads.html
+++ b/docs/dyn/gmail_v1.users.threads.html
@@ -131,9 +131,9 @@
         "historyId": "A String", # The ID of the last history record that modified this message.
         "payload": { # A single MIME message part. # The parsed email structure in the message parts.
           "body": { # The body of a single MIME message part. # The message part body for this part, which may be empty for container MIME message parts.
-            "data": "A String", # The body data of a MIME message part. May be empty for MIME container types that have no message body or when the body data is sent as a separate attachment. An attachment ID is present if the body data is contained in a separate attachment.
+            "data": "A String", # The body data of a MIME message part as a base64url encoded string. May be empty for MIME container types that have no message body or when the body data is sent as a separate attachment. An attachment ID is present if the body data is contained in a separate attachment.
             "attachmentId": "A String", # When present, contains the ID of an external attachment that can be retrieved in a separate messages.attachments.get request. When not present, the entire content of the message part body is contained in the data field.
-            "size": 42, # Total number of bytes in the body of the message part.
+            "size": 42, # Number of bytes for the message part data (encoding notwithstanding).
           },
           "mimeType": "A String", # The MIME type of the message part.
           "partId": "A String", # The immutable ID of the message part.
@@ -173,7 +173,7 @@
 Args:
   userId: string, The user's email address. The special value me can be used to indicate the authenticated user. (required)
   labelIds: string, Only return threads with labels that match all of the specified label IDs. (repeated)
-  q: string, Only return threads matching the specified query. Supports the same query format as the Gmail search box. For example, "from:someuser@example.com rfc822msgid: is:unread".
+  q: string, Only return threads matching the specified query. Supports the same query format as the Gmail search box. For example, "from:someuser@example.com rfc822msgid: is:unread". Parameter cannot be used when accessing the api using the gmail.metadata scope.
   pageToken: string, Page token to retrieve a specific page of results in the list.
   maxResults: integer, Maximum number of threads to return.
   includeSpamTrash: boolean, Include threads from SPAM and TRASH in the results.
@@ -193,9 +193,9 @@
             "historyId": "A String", # The ID of the last history record that modified this message.
             "payload": { # A single MIME message part. # The parsed email structure in the message parts.
               "body": { # The body of a single MIME message part. # The message part body for this part, which may be empty for container MIME message parts.
-                "data": "A String", # The body data of a MIME message part. May be empty for MIME container types that have no message body or when the body data is sent as a separate attachment. An attachment ID is present if the body data is contained in a separate attachment.
+                "data": "A String", # The body data of a MIME message part as a base64url encoded string. May be empty for MIME container types that have no message body or when the body data is sent as a separate attachment. An attachment ID is present if the body data is contained in a separate attachment.
                 "attachmentId": "A String", # When present, contains the ID of an external attachment that can be retrieved in a separate messages.attachments.get request. When not present, the entire content of the message part body is contained in the data field.
-                "size": 42, # Total number of bytes in the body of the message part.
+                "size": 42, # Number of bytes for the message part data (encoding notwithstanding).
               },
               "mimeType": "A String", # The MIME type of the message part.
               "partId": "A String", # The immutable ID of the message part.
@@ -275,9 +275,9 @@
         "historyId": "A String", # The ID of the last history record that modified this message.
         "payload": { # A single MIME message part. # The parsed email structure in the message parts.
           "body": { # The body of a single MIME message part. # The message part body for this part, which may be empty for container MIME message parts.
-            "data": "A String", # The body data of a MIME message part. May be empty for MIME container types that have no message body or when the body data is sent as a separate attachment. An attachment ID is present if the body data is contained in a separate attachment.
+            "data": "A String", # The body data of a MIME message part as a base64url encoded string. May be empty for MIME container types that have no message body or when the body data is sent as a separate attachment. An attachment ID is present if the body data is contained in a separate attachment.
             "attachmentId": "A String", # When present, contains the ID of an external attachment that can be retrieved in a separate messages.attachments.get request. When not present, the entire content of the message part body is contained in the data field.
-            "size": 42, # Total number of bytes in the body of the message part.
+            "size": 42, # Number of bytes for the message part data (encoding notwithstanding).
           },
           "mimeType": "A String", # The MIME type of the message part.
           "partId": "A String", # The immutable ID of the message part.
@@ -329,9 +329,9 @@
         "historyId": "A String", # The ID of the last history record that modified this message.
         "payload": { # A single MIME message part. # The parsed email structure in the message parts.
           "body": { # The body of a single MIME message part. # The message part body for this part, which may be empty for container MIME message parts.
-            "data": "A String", # The body data of a MIME message part. May be empty for MIME container types that have no message body or when the body data is sent as a separate attachment. An attachment ID is present if the body data is contained in a separate attachment.
+            "data": "A String", # The body data of a MIME message part as a base64url encoded string. May be empty for MIME container types that have no message body or when the body data is sent as a separate attachment. An attachment ID is present if the body data is contained in a separate attachment.
             "attachmentId": "A String", # When present, contains the ID of an external attachment that can be retrieved in a separate messages.attachments.get request. When not present, the entire content of the message part body is contained in the data field.
-            "size": 42, # Total number of bytes in the body of the message part.
+            "size": 42, # Number of bytes for the message part data (encoding notwithstanding).
           },
           "mimeType": "A String", # The MIME type of the message part.
           "partId": "A String", # The immutable ID of the message part.
@@ -383,9 +383,9 @@
         "historyId": "A String", # The ID of the last history record that modified this message.
         "payload": { # A single MIME message part. # The parsed email structure in the message parts.
           "body": { # The body of a single MIME message part. # The message part body for this part, which may be empty for container MIME message parts.
-            "data": "A String", # The body data of a MIME message part. May be empty for MIME container types that have no message body or when the body data is sent as a separate attachment. An attachment ID is present if the body data is contained in a separate attachment.
+            "data": "A String", # The body data of a MIME message part as a base64url encoded string. May be empty for MIME container types that have no message body or when the body data is sent as a separate attachment. An attachment ID is present if the body data is contained in a separate attachment.
             "attachmentId": "A String", # When present, contains the ID of an external attachment that can be retrieved in a separate messages.attachments.get request. When not present, the entire content of the message part body is contained in the data field.
-            "size": 42, # Total number of bytes in the body of the message part.
+            "size": 42, # Number of bytes for the message part data (encoding notwithstanding).
           },
           "mimeType": "A String", # The MIME type of the message part.
           "partId": "A String", # The immutable ID of the message part.