Style the Footer for the landing page

* Add footer partial
* Add FontAwesome support
* Add copy for footer
* Add thoughtbot logo

![middleman-footer](https://cloud.githubusercontent.com/assets/816402/4909369/ca538cde-6472-11e4-9a0f-b2857c0d40e0.png)

for organization, i would suggest making a components or modules folder to hold all of these files, and creating a manifest scss file to import them, then import that manifest here

for example
`@import "modules/modules"`

then in the file `source/stylesheets/modules/_modules.scss`
```
@import "layout"
@import "hero";
@import "top-nav";
@import "browser";
@import "footer";
```
then move all of the above files into the /modules directory