Adafruit-circuitpython-tsl2561

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-tsl2561`.

Read the [docs](http://circuitpython.readthedocs.io/projects/tsl2561/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).

To use in CPython, `pip3 install adafruit-circuitpython-tsl2561`.

Read the [docs](http://circuitpython.readthedocs.io/projects/tsl2561/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`

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-tsl2561`.

Read the [docs](http://circuitpython.readthedocs.io/projects/tsl2561/en/latest/) for info on how to use it.

Thanks to dhalbert for finding the issue. Thanks to jerryneedell and caternuson for getting it fixed up!

Resolves:
- Fixes lux calculation to accept ratio of 0
- Simplifies if/elif tests to only test upper limit on each case

Thanks to tannewt for the great work!

Release with binaries for CircuitPython 2.x. Note this might not work with CircuitPython 3.0+!