- Change part of the install generator to `rails_config:override` that creates an config/rails_config.rb initializer and disables the default initialzer

DONE:
- Add a Rails before_filter that triggers Settings.reload! for each development request
- Add generator `rails_config:install` to create the default setting files
- Allow user to customize the name of the global setting object (Settings)
- Abstract OpenStruct to RailsConfig::Options
- Add ability to define multiple sources (Start with YAMLSource)