Add 'objectify' function to convert dicts and appstructs back into SQLAlchemy models

See #20.

This pull request adds the 'objectify' function which accepts a data structure (or appstruct) and converts the data back into mapped SQLAlchemy objects.  This function also accepts a `context`, which when provided, acts as the base object for updating attributes -- so updating a SQLAlchemy model already associated with a session, for instance, is simple.

Some other minor changes as well.  

On a slightly separate note, with regards to releases, I noticed that 0.2 was missing from the change log.   I use https://pypi.python.org/pypi/zest.releaser to manage all my Python egg releases since it handles auto-updating of version numbers, updating change logs with release data, uploading to PyPI, tagging in VCS, and more (or any combination) - in a single command.  IMHO, it's worth using for release consistency and saving time.