Rename executable to adafruit-nrfutil

Executable name now uses a hyphen instead of an underscore, to match the project name: adafruit-nrfutil.

Appveyor integration to build Windows standalone executable.

First release for pypi

Conversion to Python 3, with automatic deployment to pypi. The excutable is now named

adafruit_nrfutil

Install from the command line:

pip3 install --user adafruit-nrfutil

or, on Windows:

pip install adafruit-nrfutil

0.5.2d

compatible with Arduino BSP 0.8.x