Adafruit-circuitpython-ds18x20

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

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

To use in CPython, `pip install adafruit-circuitpython-ds18x20`.

Read the [docs](http://circuitpython.readthedocs.io/projects/ds18x20/en/latest/) for info on how to use it.

Thanks to sommersoft and kattni for updating the README.

To use in CircuitPython, download the .mpy file and copy it to the `lib` folder on the `CIRCUITPY` drive. Or, simply install the [Adafruit CircuitPython bundle](https://github.com/adafruit/Adafruit_CircuitPython_Bundle).

Read the [docs](http://circuitpython.readthedocs.io/projects/ds18x20/en/latest/) for info on how to use it.

Thanks to sommersoft for the great work!

Thanks to brentru for the great work!

Initial release to trigger mpy generation with Travis CI.