PEP-8, Python 3, and documentation
Fairly large refactor...

- more flexible shebang
- restart haproxy directly rather than using shell script
- check that haproxy is installed and on the PATH before running
- more docs
- connect to etcd once
- created main() function
- simplified main procedure
Removed script to reload haproxy
Merge branch 'master' of github.com:charford/docker-discover

Conflicts:
	main.py