add new plugin `GitHub Git Transmit`

Add new typecho post from git/GitHub.
GitHubGit: add actual action logic

It works on 0.9(13.12.1).
GitHubGit: simple documentation
Merge pull request #1 from weakish/master

GitHubGit
Merge pull request #2 from mutoo/master

add LaTex Plugin
Merge branch 'master' of https://github.com/typecho/plugins
Merge branch 'master' of https://github.com/mutoo/plugins
upgrade LaTex Plugin: customize ```mark enabled