Add support for x-www-form-urlencoded

[chickahoona]

Currently it is not possible to specify parameters and "x-www-form-urlencoded" them.

As an example:

body:
  application/x-www-form-urlencoded:
    properties:
      name:
        description: name on account
        type: string
        example: Naruto Uzumaki
      gender:
        enum: ["male", "female"]

This renders to:

Instead it should show an example like:

curl -d "name=Naruto Uzumaki&gender=male" -X POST https://example.com/oauth2/token

This is especially problematic, as one wants to describe an oauth flow, which "x-www-form-urlencoded" its parameters.

Sidenote: It was also requested here: https://github.com/raml2html/raml2html/issues/386

[wdullaer]

This would require some additional features in the template and the formatting code.
It's a good feature request. I'm not sure if/when I'll get time to look at it though.