Made a little plugin to adds paths (links to param definitions)

My two cents:

Given that passing a `paths` option when generating Markdown format (haven't tried that with HTML output) will allow Documentation.js to automagically link said definition to the respective link, I'm building [a collection of widely used parameter types](https://www.npmjs.com/package/param-links).

I started out adding GeoJson types as [Turf.js does](https://github.com/Turfjs/turf/blob/master/documentation.yml#L158-L192)

(I'm using node api, by the way)