Adafruit-circuitpython-74hc595

This release includes:
* Migrating this repository from Travis to GitHub Actions. This has no effect on the behavior of the code itself.

To use in CircuitPython, simply install the [Adafruit CircuitPython bundle](https://circuitpython.org/libraries).

To use in CPython, `pip3 install adafruit-circuitpython-74hc595`.

Read the [docs](http://circuitpython.readthedocs.io/projects/74hc595/en/latest/) for info on how to use it.

Instead of using Travis for testing PRs, this repository will now use Github Actions.

To use in CircuitPython, simply install the [Adafruit CircuitPython bundle](https://github.com/adafruit/Adafruit_CircuitPython_Bundle).

To use in CPython, `pip3 install adafruit-circuitpython-74hc595`.

Read the [docs](http://circuitpython.readthedocs.io/projects/74hc595/en/latest/) for info on how to use it.

- Added `setup.py`
- Added PyPI release info to `.travis.yml`
- Updated `requirements.txt`
- Added a more comprehensive `.gitignore`
- Updated `README` with PyPI install instructions

To use in CircuitPython, simply install the [Adafruit CircuitPython bundle](https://github.com/adafruit/Adafruit_CircuitPython_Bundle).

To use in CPython, `pip3 install adafruit-circuitpython-74hc595`.

Read the [docs](http://circuitpython.readthedocs.io/projects/74hc595/en/latest/) for info on how to use it.

To use in CircuitPython, simply install the [Adafruit CircuitPython bundle](https://github.com/adafruit/Adafruit_CircuitPython_Bundle).

Read the [docs](http://circuitpython.readthedocs.io/projects/74hc595/en/latest/) for info on how to use it.