Prepare for 17.0.0 (#615)

* Prepare for 17.0.0

Fix a bunch URLs and account for the non-existance of 16.3.

* Fix codecov link
diff --git a/src/OpenSSL/crypto.py b/src/OpenSSL/crypto.py
index 165f918..b90f0e4 100644
--- a/src/OpenSSL/crypto.py
+++ b/src/OpenSSL/crypto.py
@@ -1538,7 +1538,7 @@
           For example, you can determine if a certificate was valid at a given
           time.
 
-        .. versionadded:: 16.3.0
+        .. versionadded:: 17.0.0
 
         :param datetime vfy_time: The verification time to set on this store.
         :return: ``None`` if the verification time was successfully set.