Adding support for request bodies and nested parameters for PUT and POST method request bodies.

Ref: #3, #9, #51, #66 

This patch adds support for documenting parameters of a request body. As
values are filled into the content parameters, the method's text area is
filled in with what the request body should be. The text area is what
will be submitted as the request body, and can be modified directly if a
user wants to.