Add setup.py and other packaging files

[bleykauf]

I noticed that PiPyADC is currently not in pypi. Since I am currently building a programm based on PiPyADC I wanted to install it as a package and added the necessary files install instructions to the README in my fork.

I think it would be useful to others to merge these changes to your official repo. I can also assist you in pushing it to pypi.org if you want. Then it could simply be installed with pip.

I made the following changes:

• changed to repo layout:
  • dedicated example and package folders
  • fixed relative imports
• added setup.py and setup.cfg, MANIFEST.in and pyproject.toml
• added automatic versioning with versioneer (https://github.com/python-versioneer/python-versioneer)
• removed some unneccesary sudos in the README, adjusted install instructions and make distictions between python 2 and 3 more explicit
• tested on a Raspberry Pi 3 for both Python 2.7.16 and 3.7.3

Note that the URLs and maintainer info have to be changed to in the setup.cfg and README.md.