Fix issues with python 3 on windows and linux

[rikardn]

Some fixes that was needed for me to get Inline::Python to work with Winpython and to play better with python 3.

• Prefer python 3 if available (will simplify transition to python 3 for many linux distributions)
• Also look for executable with name python3
• Fix issues with getting python libpath with winpython
• Fix issues with python lists and tuples not being transferred to perl properly

I have tested everything on Ubuntu 19.04 using python 2.7.16 and python3 3.7.3 and Windows 10 using winpython 3.7.4

It would be super if these fixes could go up on CPAN. Please let me know if I could give any further help to this end.

[hakonhagland]

@rikardn Thanks for the fix!

Maybe consider uploading this to CPAN ? On my machine (Ubuntu 21.04) there is no python executable, only python2 and python3 (in /usr/bin) so when I run (from CPAN distribution):

$ perl Makefile.PL
Found these python executables on your PATH:
Use which? [1] 
Invalid number. Please enter only numbers from 1 to 0 or the full path to your python executable.
Set the INLINE_PYTHON_EXECUTABLE environment variable to the full path to your python executable to avoid this question.

it does not find anything at all.