Make Geocoder.configure accept a hash (now preferred) and add
Geocoder.config method (for reading config). Deprecate old syntax.

This fixes issue #244.

Geocoder.coordinates sometimes returns nil which causes crashes in the distance
and bearing calculations. By returning a point array of [ NaN, NaN ] this
distances will be also NaN which seems to be a sensible result. If the argument
to extract_coordinates has an unexpected form, also return [ NaN, NaN ].

It's not an ideal name either, but it's short and it's slightly more
specific than "method".

This reduces the desire to use map! (instead of map) which would modify
the user's argument in-place. There's a test to prevent that but this
makes sense semantically too.

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.

Also clean up code comments.

This allows easier substitution of custom values.

This was yielding incorrect bearing calculations (east and west were
treated as the same direction).

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'])

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

Move some methods into it (organize!).