This addresses issue #199 and is more directly a response to the
excellent comments from github.com/zetetic on commit 1b658304.

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This change will call the writer methods defined on an AR model, if they're
implemented, instead of going behind their back. This also avoids a rails 3
deprecation warning, if the named attributes aren't actually database
attributes.

do not redefine "type" method

it is better and faster

The `del` method must be defined on the cache store too

Deprecate 'class' method for Nominatim result instance

Fixes bug in -j and -u options.

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.