Substituted assert statements for exceptions, allowing for use of the `-O` flag while compiling to `.mpy`. Thanks bill88t!
To use in CircuitPython, simply install the [Adafruit CircuitPython Bundle](https://circuitpython.org/libraries).
To use in CPython, `pip3 install adafruit-circuitpython-wiznet5k`.
Read the [docs](http://circuitpython.readthedocs.io/projects/wiznet5k/en/latest/) for info on how to use it.