- set VERSION to 3.1.0 (introduce a patch level 0 so that it becomes
easier to publish packages with small fixes, eg for installation)
- got rid of ancient ez_install: just use pip
- updated README and INSTALL
- updated classifiers in setup.py (license: LGPL v2.1 and other meta data);
updated URL to point to http://propka.org because unlike http://propka.ki.ku.dk
it is not completely dead and has a link to the pdb2pqr propka server as well
as the GitHub page
