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 
Yeah. I can see that. I like the idea of it using the </> notation, but calling it min/max then seems weird. I wonder if we could do it as something like `Range: 0 <= value` and/or `Range: 0 <= value <= 1` or something like that. What do you think?