incorporate micromodels with no functional changes

Pulled in the micromodels code from https://github.com/j4mie/micromodels
changing only the namespace and the name of the tests file.
list issues to be resolved

Went through the code, dropping lots of FIXME and TODO markers.
make tests pass on py27 and py33

Metaclass for model now uses six for py2-py3 compatibility.

Eliminated incompatible PySO8601 in favor of python-dateutil and pytz.
Sadly, although dateutil's parser is compatible, the tz lib is not, at
least as of 2.2.

Fixed other syntactic differences (unicode, iteritems).
test model inheritence

Added test for model inheritence implemented in the new metaclass.

Split the fields tests into a separate file because it was getting huge.
make constructor take kwargs like a normal class

Removed the from_kwargs class method and just made the standard
constructor take kwargs, as any normal class would do.
fix some doctest/pep8 complaints
remove source attr from fields
make TimeField hand datetime values
make BooleanField more consistent with Python

BooleanField now obeys Python's bool() with one exception: if the value
is a string containing "false" or "0" then it evaluates false.
Merge branch 'master' into micromodels
tox update, more pythons
Remove model instance data from Field instances

Interface was inconsistent and problematic, with to_serial taking an
argument but to_python using data shoved into the Field via populate().
Modified to work more like Django field, eliminating the populate()
method and passing the data to to_python explicitly.
Make basic Fields handle None values

Improved test coverage and case coverage. Each Field should now
correctly handle None values and values of the correct type that require
no conversion.
Corrections to setup.py and README

Corrected the license and description, added trove classifiers.
rst2html fix
Prevent metaclass from squelching docstring
Update docs

Undocumented the complex fields for now. Removed some superfluous
docstrings. Made classes autodoc their members.