Initial python3 changes

Mostly just updating libraries, removing string encoding/decoding,
fixing some edge cases. No new functionality was added in this
commit.

lib/requests_oauthlib/compliance_fixes/mailchimp.py

@@ -0,0 +1,23 @@
+import json
+
+from oauthlib.common import to_unicode
+
+
+def mailchimp_compliance_fix(session):
+    def _null_scope(r):
+        token = json.loads(r.text)
+        if "scope" in token and token["scope"] is None:
+            token.pop("scope")
+        r._content = to_unicode(json.dumps(token)).encode("utf-8")
+        return r
+
+    def _non_zero_expiration(r):
+        token = json.loads(r.text)
+        if "expires_in" in token and token["expires_in"] == 0:
+            token["expires_in"] = 3600
+        r._content = to_unicode(json.dumps(token)).encode("utf-8")
+        return r
+
+    session.register_compliance_hook("access_token_response", _null_scope)
+    session.register_compliance_hook("access_token_response", _non_zero_expiration)
+    return session