Added formatting options to __unicode__, __repr__

    * `Model.__identifiers__` is an optional property which, when set,
      can describe the fields on the model to be used when constructing
      a representation.
Added helper functions for `Hashable`

    * Easily create foreign key columns and association tables which
      follow a standard naming convention
Major modifications to `Storable`

    * Adding `batteries.path` module, which is a rip of `pyramid.path`,
      less any pyramid dependencies (none of them were critical)
    * `Storable` now configures itself by hooking events, using the
      `sqlalchemy.event.listens_for` decorator
Added `Loggable` class

    * Optional or required logging on `before_insert`, `before_update`
    * `LogMessage` subclass to descend from for log message