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 
True. I guess I just worried that removing it now would already be backwards-incompatible. But perhaps it hasn't been around long enough for people to be using it. I'm fine removing it here and re-evaluating if/when we need to.