Documentation 0.4.0

[ricekab]

After tests are implemented (and all ok). Update documentation on new structure.

[ricekab]

As found in #9 -- Incorrect example in documentation (0.3.0): http://sqlalchemy-seeder.readthedocs.io/en/latest/usage.html#data-format

The class should be seperated from the module using a colon (:), not a dot (.)