save all the oauth2 providers in a single map & github oauth2 provider added
Merge remote-tracking branch 'upstream/master'
get oauth2 needed package doc added to README.md
get oauth2 needed package documented to README.md
Merge branch 'master' of https://github.com/hippasus/ohlala
load screen_name for sina provider
show third party profile(image/name) on /user/bind page
1. let user to input name in /user/bind
2. save third party avatar url and link in milnk db
make ThirdPartyProvider & OAuth2Provider as public so that other package can implement & install new providers to milnk system.
fix the bug that cookie not cleared after manual bind third party user done.
Merge pull request #27 from hippasus/master

第三方账户登录的一些改进