#200 First attempt at API cleanup to match OAuth1.
Updated request_validator documentation to include credential-saving methods

There are methods in request_validator that must be implemented and that aren't listed in the class's documentation. Also fixed a couple of minor documentation typos.
Merge pull request #199 from squirly/master

The authorization endpoint now returns a 200 on "oob" oauth_callbacks.
Merge pull request #203 from kdazzle/patch-1

Updated request_validator documentation to include credential-saving met...
Merge pull request #201 from squirly/#200

OAuth2 API cleanup to match OAuth1. Proposal for Issue #200