Add a bunch of features

[AnthonySuper]

This PR would do the following:

1. Replace HAML with ERB
2. Add the ability to document attributes of a response individually
   1. Allow nesting of attributes
   2. Allow enum attributes, where the attribute must be one of a predefined set of values. Also allows you to document what those attributes mean.
3. Add the ability to generate an example response from the documented attributes of a response
4. Add the ability to define a common sub-type (probably should rename that to sub-object), which you can use for documentation across multiple responses
5. Adds styles to the added features

This is kind of a lot of code, and the updated README and Documentation (generated with rake doc) should explain things in more detail.

[droptheplot]

Thanks.