Fix to #nearbys when activerecord model has a primary key different than 'id'

Fixes: #194 - add_exclude_condition breaks on tables without ID field - https://github.com/alexreisner/geocoder/issues/194

Support for #near(..., :select => :ignore)

Also rename :ignore to :geo_only (more descriptive/specific--we might
introduce other options in the future and :ignore is kind of vague).

Fix documentation for within_bounding_box arguments

Fix within_bounding_box() method parameter; Only box is needed and no need of distance.

in request to geocoding service.

Also move some lookup-related methods to Geocoder::Lookup module.

This is in preparation for adding Maxmind as an IP lookup.

Conflicts:
	lib/geocoder/lookups/base.rb

Conflicts:
	lib/geocoder.rb

Removed state from city.

Thanks github.com/johanneswuerbach.

Thanks github.com/johanneswuerbach.

Fixed unit config not working with sqlite distance