Changed signature to match the builtin for CircuitPython. This is an API-breaking change, but shouldn't impact existing libraries or guides,
To use in CircuitPython, simply install the [Adafruit CircuitPython Bundle](https://circuitpython.org/libraries).
To use in CPython, `pip3 install adafruit-circuitpython-pixelbuf`.
Read the [docs](http://circuitpython.readthedocs.io/projects/pixelbuf/en/latest/) for info on how to use it.