Adding ability to pass query options to the Mapbox API

[quinnchr]

This is a fairly simple change to pass along options to the Mapbox API. All options that are set are passed directly to the API, except for the proximity option which will also accept L.latLng objects. This allows you to do something like:

Geocoder.mapbox('pk.blahblahblah', { geocodingQueryParams: {
    country: 'US',
    proximity: map.getCenter()
}})

[perliedman]

Hi and thanks, this looks great! I added a quick comment, tell me what you think.

[perliedman]

What do you think about moving this check to the geocode method, so that it will work even if the options are updated after the control has been initialized?

I would thing it's quite common to set the proximity option to the map's center or similar, so that it will be updated as the user moves around.

[quinnchr]

It definitely makes more sense to handle the proximity param inside the geocode function. Thanks for the idea! The latest commit should take care of it. Let me know if there's anything else this needs.

[perliedman]

Thanks again, great addition!