Add bourbon

:warning: WIP do not merge :warning: 
- [x] Waiting some approval here
- [x] Add features
- [x] Add CHANGELOG

This is a proposal to add bourbon and his family as default on pah. This way when I start a app and add a simple html I already have a good default to start like this.

```slim
h1 Welcome#index
p Find me in app/views/welcome/index.html.slim
h2 Hi i am a H2
p  Lorem ipsum dolor sit amet, consectetur adipiscing elit. Fusce ut ante turpis. Morbi iaculis libero sed nunc euismod ornare id non mi. Curabitur vitae bibendum ante. Nulla facilisi. Proin rhoncus, enim eget mattis sollicitudin, arcu lectus ultrices ligula, vitae fringilla eros nisl vel dolor. Fusce euismod aliquet ligula, vitae vehicula purus auctor nec. Praesent lectus sapien, fringilla id rhoncus nec, lacinia non lorem. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Fusce sit amet scelerisque magna. Nulla sit amet porta orci.
h3 Hi i am a H3
h4 Hi i am a H4
h5 Hi i am a H5
h6 Hi i am a H6

table
  thead
    tr
      th Name
      th Email
  tbody
    tr
      td Mauro
      td mauro@helabs.com.br
```

![captura de tela 2014-06-27 as 17 56 02](https://cloud.githubusercontent.com/assets/260746/3417813/879d5370-fe3d-11e3-8079-e38159961c53.png)

And all the others styles defined by bitters as you [can see here](http://bitters.bourbon.io/images/bitters-example.jpg). Besides the mixins of bourbon, the neat grid, and the generator of patterns reffils.

A by product by bitters is the good practice of creating css files, [since his organization is pretty cool](https://github.com/thoughtbot/bitters/tree/master/app/assets/stylesheets). I talk more about [bourbon and his family here](http://helabs.com.br/blog/2014/06/27/rails-front-end-com-bourbon-e-sua-familia/).

cc/ @mergulhao @TiuTalk @Helabs/designers