Add support for config file and minimum and maximum values in docs

Allows you to supply a config file via `prmd -s prmd-config.json` and override any of the other settings you would supply. This also supports YAML config files.

Couple of extra bonus things:
* Remove the url style parameter from the command line and only supply it via the config file.
* Add support for `minimum` and `maximum` parameters to be displayed in the docs
* Little bug fix 
This was taken directly from Active Resource: http://apidock.com/rails/v4.0.2/Hash/deep_symbolize_keys
I didn't really want to include Active Resource for dependency bloat reasons.
I could rewrite this to be a non core extension if you want