Hash order needs to be preserved so with Ruby 1.8 we use a
BSON::OrderedHash instead of a generic one.

Mongoid is not technically an ORM (they call it an "Object Document
Mapper"), and we might support other such storage mechanisms in the
future.

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.

Multiply by .707 (sin(45)) instead of .5.

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