Merge branch 'release/0.2.3' into develop
* Added some starting documentation
* Removed unused code
* Added a test for an aggregate wrapper method

* Fixed all aggregate class references
* Return int from count method

* Finished count test
* Added tests for average, sum, min, max
* Removed unused method
* Return self from wrapping query
* Added test for wrap
* Added cast and distinct params to field init and updated tests
* Added casting to fields
* Added tests for custom sql and sql args
* Added test for explain
* Fixed pep8 errors
* Fixed pyflakes errors
* Added documentation to Query class
* Handle different types for field param
* Documented from_table method
* Moved doc strings to instance variables
* Added documentation to join method