Implement interface to Rietveld. This is a simple python interface based on Rietveld's HTTP interface, which is being accessed via OAuth2 tokens generated for a service account authenticated via an RSA key. R=agable@chromium.org Review URL: https://codereview.chromium.org/20495003 git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/reviewbot@215841 0039d316-1c4b-4281-b951-d872f2087c98