Added support for inverted clocks, thanks so much to mfhepp for the contribution!
To use in CircuitPython, simply install the [Adafruit CircuitPython Bundle](https://circuitpython.org/libraries).
To use in CPython, `pip3 install adafruit-circuitpython-si5351`.
Read the [docs](http://circuitpython.readthedocs.io/projects/si5351/en/latest/) for info on how to use it.