I've added the ability to change the translation mechanism

I added a new cattr_accessor to store the translator function.  In fact, this can be any method that responds to call.  If one is not present then it just does a .to_s on the text that is originally passed in.

The reason we require this is because we want to do some custom organization of breadcrumbs within I18n and tie them closely to our page titles and headers.  I need to have complete control over the translation mechanism.

I've written full tests and documentation.