Currently, `src/top_evil_rs.py' script recursively scans current
directory for Rust sources and print statistics about them.
When run from git root, it also scans target/ directory, which is
useless.
This commit add cludge that checks if script is run from git root
directory, and `chdir' into `src/' before performing actions.
Unprincipled, but convenient.
PEP-0394 (https://www.python.org/dev/peps/pep-0394/) recommends to use more specific shebangs.
For example, Debian allows /usr/bin/python to be configured to python2 via `update-alternatives python`, but the script does not work with Python 2.
