Add HTML whitespace remover

Use case:

HTML document 1: http://resurtm.com/yii-stuff/spaceless-use-case-1.html
HTML document 2: http://resurtm.com/yii-stuff/spaceless-use-case-2.html

Diff between them:

```
$ diff spaceless-use-case-1.html spaceless-use-case-2.html
43c43,44
<               </div><div class="right">
---
>               </div>
>               <div class="right">
```