Adafruit-circuitpython-ads1x15

- 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-ads1x15`.

Read the [docs](http://circuitpython.readthedocs.io/projects/ads1x15/en/latest/) for info on how to use it.

Adds a polling loop to wait for conversion to complete.

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Thanks to sommersoft for the great work!

Thanks to brentru for the great work!

Initially left the file __init__.py out of the library sub folder. This release adds it in. Also, files have been updated for new build process.