I noticed this option was in the README, but not in the template, so it
might be nice to have it generated in the template as well.

cache must respond to #del, not #keys

TimeoutError is deprecated in Ruby 2.3.0. It has been an alias for
Timeout::Error starting in Ruby 1.8.0, and should be safe to replace.

Move away from generating a `geocoder.rb` initializer with old school ruby hash syntax in favor of the new/current style.

See: https://github.com/alexreisner/geocoder/issues/703

Need increased specificity to support other MaxMind packages.

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