This update allows the library to be used with CPX+Gizmo and other devices without the `json` module.
To use in CircuitPython, simply install the [Adafruit CircuitPython bundle](https://circuitpython.org/libraries).
To use in CPython, `pip3 install adafruit-circuitpython-slideshow`.
Read the [docs](http://circuitpython.readthedocs.io/projects/slideshow/en/latest/) for info on how to use it.