Drastically increase coverage by checking repr() (#1521)

A lot of our missing coverage is caused by not checking repr(), which is
trivial enough to test against -- do so, and also clean up existing repr
tests to look the same by calling repr(). Where it was trivial, add a
few assertions about missing attributes.

github/RateLimit.py

@@ -50,7 +50,7 @@ class RateLimit(github.GithubObject.NonCompletableGithubObject):
             is present in the rate object.
         """
     )
-    def rate(self):
+    def rate(self):  # pragma: no cover
         """
         (Deprecated) Rate limit for non-search-related API, use `core` instead