Implement AbortController/AbortSignal pattern

[xivk]

I was wondering if it would be useful to do a pull request implementing a version of the geocode call accepting an AbortSignal?

We use it to cancel requests that have not completed yet, for example when the user does a new search before the previous result is available. This improves performance and stops useless requests from being sent and then ignored.

[tsamaya]

I think that would be great.
Did you see: I was also considering removing the cross-fetch dependency in version 2 of lib #222.