Python 3 compatibility

[slayoo]

See also: https://sourceforge.net/p/gnudatalanguage/bugs/574/
(pointing out that CMakeModules/FindNumpy.cmake uses Python-2 syntax of print)

[eatdust]

One can select explicitly the python version with:
-DPYTHONVERSION=2
-DPYTHON_EXECUTABLE=/usr/bin/python2

and in 0.9.8, this works fine, also with python3. However, In view of python2 being obsoleted, python3 should be supported, but compilation with python3 fails at multiple places afterwards.

Cheers.

[opoplawski]

For the record - the FindNumpy.cmake issue was addressed with f997bac