Support Qiita:Team
Fix document structure

`md` helper generates block-level elements, so don't include it inside `p` element.
Improve instructions
Disable mention filter

The user name of Qiita:Team is not necessarily the same as it of GitHub.
Cosmetic
Merge pull request #1 from ursm/support-qiita-team

Some improvements for Qiita:Team hook
Change user_url, unnecessary to parse base_url :P
Merge pull request #5 from hanachin/support-qiita-team

Support Qiita:Team