Adafruit-circuitpython-pcf8523

- 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-pcf8523`.

Read the [docs](http://circuitpython.readthedocs.io/projects/pcf8523/en/latest/) for info on how to use it.

Thanks to tannewt for the great work!

Added demo.py to examples folder

Thanks to tannewt for the great work!

Changes made to follow changes in Adafruit_Circuitpyton_BusDevice.I2CDevice

This requires [CircuitPython](https://github.com/adafruit/circuitpython/releases) 0.9.4+!

Initial release of the driver with full support for the RTC.