python: add interpreter names to python parser definition

This achieves the request submitted at ctags-users mailing list:

    [Ctags] Shebang with python3 instead of python
     From: Martin Ueding <dev@ma...> - 2013-01-26 18:36:32

Signed-off-by: Masatake YAMATO <yamato@redhat.com>
Merge pull request #54 from masatake/sf-ctags-user-list-shebang-with-python3-instead-of-python

python: add interpreter names to python parser definition