More supported argument types

This will allow both enumerated fields and boolean fields to generate the correct fields for IODocs, as well as all default values to be set.

Examples:
----------------

```ruby
##
# Create a post
#
# URL [POST] /posts
#
# @argument [String] title The title of the post (REQ)
# @argument [Text] body The body of the post
# @argument [Boolean] published Is the post published? (REQ) (Default: false)
# @argument [EnumeratedField] post_type The type of post (Values: 'tweet','article','rage fest')
def create
end
```