Initial python3 changes

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

lib/oauthlib/oauth2/rfc6749/clients/__init__.py

@@ -0,0 +1,14 @@
+# -*- coding: utf-8 -*-
+"""
+oauthlib.oauth2.rfc6749
+~~~~~~~~~~~~~~~~~~~~~~~
+
+This module is an implementation of various logic needed
+for consuming OAuth 2.0 RFC6749.
+"""
+from .backend_application import BackendApplicationClient
+from .base import AUTH_HEADER, BODY, URI_QUERY, Client
+from .legacy_application import LegacyApplicationClient
+from .mobile_application import MobileApplicationClient
+from .service_application import ServiceApplicationClient
+from .web_application import WebApplicationClient