Get and use the Python lib path for CMake. closes #31

Fix non standard python lib path when libpythonX.Y.so is not in '/usr/lib'
(Debian multiarch for instance). Use the 'LIBPL' variable from
'disutils.sysconfig' and add it to the list of paths to find the library.
Merge remote-tracking branch 'garaud/cmake-python'
Add a comment that LIBPL is for Linux/Debian Jessie