Merge pull request #16 from mulixiang199016/master

user following questions and change maiil to askrubyist.org
Refactor the User model.
refactor questions.js.coffee.
Refactor session_filter.
Move markdown from ApplicationHelper to lib directory.
Refactor the User model complex method.
Allow password idenfity user to bind github account.
Modify the edit view to support bind and unbind thirdparty account.
add tag widgets(show tag as tag's question count DESC and hide none question's tag)
Merge remote-tracking branch 'upstream/master'