Support pluggable RuleFactory

[davidpadbury]

I started looking into customizing what types are being used for different types of format (particularly using Joda's LocalDate for a date format). Due to the rather elegant design of how rules are evaluated I feel that by supporting a "pluggable" rules factory, consumers would have the ability to tweak much of the behavior of how rules work in a very simple manor.

How would we feel about being able to specify a RulesFactory inheritor class as part of the Mojo properties similar to how the custom annotator is done?

[joelittlejohn]

Sounds like a good addition to me. As you say, allowing a custom RuleFactory basically allows all the generation behaviour to be customized so it's a good piece to make pluggable. Happy to add this to the next version.

[joelittlejohn]

Lets track this on #211