AUTHORS: add willh
packages: add gist for convenience

Annoyingly, the Debian package calls the binary "gist-paste", while the
Ruby gem names it just "gist".

This might actually be a good example of where our own apt repo could
come in handy.
extrapackages: remove python-argparse

python-argparse no longer exists in jessie (it's a virtual package for
libpython2.7-stdlib), and presumably we don't need it on wheezy with
python2.7 anyway.