Also add extract_coordinates method and use wherever relevant.

Reported by github.com/joelmats. The array passed to
Geocoder::Calculations.geographic_center was being modified in-place.

Get rid of space after comma, if any (Google was returning no results).

Was ignoring non-ASCII characters. Thanks to github.com/supergivi for
reporting the bug.

Also clean up code comments.

Was preventing other test from running.

Improve comments, make code style consistent with rest of Geocoder, and
remove options (keep it dead simple).

Adds methods for calculating the bearing between two points and for converting that bearing into a compass point, e.g. North or South West. If you want fewer or additional compass points (e.g. South By South West, or just NESW) provide a second parameter containing your array of points, e.g. Geocoder::Calculations::compass_point(90,['north','east','south','west'])

After further consideration, multiple results should be the default
behavior for this method. Some services only return one result (eg: any
IP-based service) but a great feature of advanced services like Yahoo
and Google is that they return an array of choices when doing a vague
search like "100 Main St" with no city, region, or country specified.

Google results don't return a 'city', so we have to look at several
fields in descending order of preference.

Now that we also support an API key for Google it makes sense for this to
be generic.

Replaces read_coordinates (private) and fixes bug in geographic center
computation (reported by github.com/jonbuda).

This was causing an exception (thanks to github.com/mikepinde).