py-requests-oauthlib: updated to 1.2.0

v1.2.0:
This project now depends on OAuthlib 3.0.0 and above. It does not support versions of OAuthlib before 3.0.0.
Updated oauth2 tests to use 'sess' for an OAuth2Session instance instead of auth because OAuth2Session objects and methods acceept an auth paramether which is typically an instance of requests.auth.HTTPBasicAuth
OAuth2Session.fetch_token previously tried to guess how and where to provide "client" and "user" credentials incorrectly. This was incompatible with some OAuth servers and incompatible with breaking changes in oauthlib that seek to correctly provide the client_id. The older implementation also did not raise the correct exceptions when username and password are not present on Legacy clients.
Avoid automatic netrc authentication for OAuth2Session.

v1.1.0:
Adjusted version specifier for oauthlib dependency: this project is not yet compatible with oauthlib 3.0.0.
Dropped dependency on nose.
Minor changes to clean up the code and make it more readable/maintainable.

(adam)