sort footnotes in parsing markdown format which is the bug in python-markdown2.

解决使用 python-markdown2 软件包解析 markdown 时对脚注没有按照文档内容排序的问题。
add another github autolink transform

增加另一种 github 提交链接的自动处理

<https://github.com/User/Procject/commit/SHA>
<http://github.com/User/Procject/commit/SHA>