Add pw_protobuf module

This change adds a pw_protobuf module containing a lightweight protobuf
wire format encoder. The encoder comes with a Python script that plugs
into protoc to generate C++ classes from Protobuf files that wrap its
functionality.

Bug: 20

Change-Id: I867655ab64c2f6ddd2a731054b1fbe7ccc97ba70
diff --git a/.pylintrc b/.pylintrc
index cac6c64..3445b61 100644
--- a/.pylintrc
+++ b/.pylintrc
@@ -356,7 +356,7 @@
 # List of members which are set dynamically and missed by pylint inference
 # system, and so shouldn't trigger E1101 when accessed. Python regular
 # expressions are accepted.
-generated-members=
+generated-members=descriptor_pb2.*,plugin_pb2.*
 
 # Tells whether missing members accessed in mixin class should be ignored. A
 # mixin class is detected if its name ends with "mixin" (case insensitive).