Updated authkey.py to inherit from object

Updated git-authorized-key/authkey.py to inherit from object so that
new-style classes are always used, even on python 2
Added support for a keyfile_location option to the git-authorized-key

Added code to get the location of the keyfiles from the config. This
avoids having to make any requirements on how the repository is setup
for this to work. Also added the print_function import from __future__
for python 2 compatibility
Renamed git-authorized-key to git_authorized_key

Renamed git-authorized-key to git_authorized_key because setuptools
doesn't like module names with dashes in them
Changed config option checkout_directory to checkout_path

Changed config option from checkout_directory to checkout_path since
that is more descriptive
Fixed multiple typos and case problems in git_authorized_keys/__init__.py
Created setup.py