Require Ruby 2.0+ (Closes #1)

RoutingFilter makes extensive use of Module.prepend which is only
available in Ruby 2.0+
Implement option to disable RoutingFilter (Closes #7)
Implement basic filter chain (Closes #4)
Implement base filter class
Implement filter interface for RouteSet (Closes #2)
Implement filter processing in router (Closes #3)
Implement a locale filter (Closes #5)