clarified shebang lines

/usr/bin/env python is unsafe; depending on your distro, it might link to any version of python.
.gitignore: added .so files
examples/retrieve.py: added argparse

IMO, this change makes the entire example a whole lot more

 - easy to use (--help FTW)
 - easy to read
added python3 support

this commit also fixes an issue where, due to non-ascii characters in my
last name, the python2 code was not actually working
(an additional 'decode' call was needed).
examples/retrieve.py: added request_balances()

mainly for testing the python3 port