Fix links to oauthlib
Merge pull request #50 from dasevilla/improve-oauthlib-links

Fix links to oauthlib
Fix typo in OAuth2Session
Fix another small typo in OAuthSession documentation
Merge pull request #51 from stephane/patch-1

Fix typo in OAuth2Session
Merge pull request #52 from stephane/patch-2

Fix another small typo in OAuthSession documentation