support setext syntax , heading and hr tag

# ChaNges

* lheading rendering
* underline rendering

## [markdown syntax guide](http://daringfireball.net/projects/markdown/basics)

```
Markdown offers two styles of headers: Setext and atx. 
Setext-style headers for <h1> and <h2> are created by 
“underlining” with equal signs (=) and hyphens (-), respectively. 
To create an atx-style header, you put 1-6 hash marks (#) 
at the beginning of the line — the number of hashes equals 
the resulting HTML header level.
```

## test markdown syntax

```
# MOU Randering

Title
-

- list1
 - list1
 - list 2
- list2

-

--test

-test

Title
=
```

### github 

![screen shot 2013-08-04 at 10 25 08](https://f.cloud.github.com/assets/1558742/906479/923fdbd8-fca7-11e2-9217-282211662b80.png)

### Markedown pro (on mac OSX)

![screen shot 2013-08-04 at 10 14 03](https://f.cloud.github.com/assets/1558742/906480/a662263e-fca7-11e2-830d-7e2942beb00c.png)

###  before marked.js rendering

![screen shot 2013-08-04 at 10 47 07](https://f.cloud.github.com/assets/1558742/906482/f3c26c2c-fca7-11e2-841e-8c03723055d8.png)

### after marked.js rendering

![screen shot 2013-08-04 at 10 49 37](https://f.cloud.github.com/assets/1558742/906483/2d568914-fca8-11e2-995c-f958085ae084.png)