Support Table Markdown Extension

Please read [here](http://misaka.61924.nl/api/#toc_0) to find the
API of misaka.

How to write tables in markdown:

* 1)

First Header  | Second Header
------------- | -------------
Content Cell  | Content Cell
Content Cell  | Content Cell

* 2)

| First Header  | Second Header |
| ------------- | ------------- |
| Content Cell  | Content Cell  |
| Content Cell  | Content Cell  |

* 3)

More details can be found [here](http://michelf.ca/projects/php-markdown/extra/#table)