Fixes dependencies and a broken link in setup.py
Fixes dependencies and a broken link in setup.py

As this project aims at Python2 (and <3.4) compatibility, I added a `version_info` check to add the correct and minimal `install_requires`.

Also, a link in the help comments was broken; fixed that too.
acrisci/i3ipc-python,chrsclmn/i3ipc-python,nicoe/i3ipc-python,xenomachina/i3ipc-python