Invoke lower on the string, don't compare the function

Previously, the function "lower" from the string object returned from
running `git config hooks.verbose` would be compared with the string
'false'. Unfortunately, this results in verbose-mode always being
enabled.
Move logic into a main() method

Although python does not require a main() method, and executes a
python program linearly, it is preferable to have a main() method and
use the name-checking idiom. This allows a python program to be
imported by other python programs, if necessary, and encourages code
modularity.
Ensure GIT_DIR is set

Add some sanity checking to ensure the environment the hook is running
in has GIT_DIR set, so as to ensure there is a git repository to
operate on.
Add an authors file for Athena

Currently, the authors file is a small subset of the people that have
Athena commit bits. It can be expanded later.
Merge branch 'debathena'