install python libraries in python site-packages directory instead of /usr/lib
Use Python Library version of the found Python Interpreter

If you have python2 at /usr/bin/python , but also
have python3 libraries and header files installed,
CMake will use the python2 interpreter, but the
python3 libraries. This causes the python libraries
found to have the same major and minor version as
the interpreter.
Merge pull request #33 from Acpharis/cmake_python

Changes to python CMake rules to find site-packages as the default install location.