generalizes routes for watching

Adds a Routes module to acts_as_watchable. This module is used in routes.rb to dynamically determine whether a requested route is one where acts_as_watchable is involved. By defining a model as acts_as_watchable, it is automatically added to the watchable routes.
adds comment to acts_as_watchable method explaining it's signature
Merge pull request #57 from opf/feature/rails3_dynamic_watchable

generalizes routes for watching