Improve default options set to improve search relevance

[scottsfarley93]

Looking at the options that are set on the geocoding call (https://github.com/mapbox/mapbox-gl-geocoder/blob/master/lib/index.js#L58), there are several defaults that could be configured to provide a better out-of-the box search experience.

Specifically, I think good improvements could be found with:

• setting trackProximity to default true -- searches with a user-relevant proximity are likely to be more relevant
• setting a default language based on the user's browser settings

I suspect this may change user's expectations and/or be a breaking change -- so we could target this for the next major release.

[andrewharvey]

I think these are positive changes.

I suspect this may change user's expectations and/or be a breaking change -- so we could target this for the next major release.

I agree.

[katydecorah]

👍 I also think that these are positive changes

[andrewharvey]

Done in https://github.com/mapbox/mapbox-gl-geocoder/tree/version4 by #200 #202, slated for v4 release.