modernized installation procedure

- 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

INSTALL

@@ -1,19 +1,11 @@
 ## Installation
 
 Clone repository or unpack the tar ball and install with
-[setuptools](http://pythonhosted.org/setuptools/index.html) (note: if
-you don't have setuptools installed you will need an internet
-connection so that the installation procedure can sownload the
-required files):
+[pip](https://pip.pypa.io):
 
-    cd propka-3.1
-    python setup.py install --user
+    pip install propka-3.1/
 
-This will install the `propka31` script in your executable directory,
-as configured for setuptools, for instance `~/.local/bin`. You can
-change the bin directory with the `--install-scripts` option. For
-example, in order to install in my `bin` directory in my home
-directory:
-
-    python setup.py install --user --install-scripts ~/bin
+This will install the `propka31` script in your executable
+directory. The `propka` Python module will also become available for
+import.