Minor setup.py issues.

I gave the nyx setup.py script a whirl today, and it mostly worked though there were 2 minor issues, both more annoying than major bugs.

• The #! line in the nyx script that gets installed should (if easy/possible) pull in the python executable name used for installation, instead of python. This is only an issue on systems that do not have /usr/bin/python, which admitedly are in a minority, but if I invoke setup.py as python2 setup.py, it would be nice if the right thing happened.
• It looks like some of the documentation installation isn't honoring the destination. The script was ran as setup.py install --user which should put everything under ~/.local, but instead the installation process croaked half way through with error: [Errno 13] Permission denied: '/usr/share/man/man1/nyx.1.gz'.