DOC: Add example Dockerfile for running a Postgres backend.
DOC: Add instructions to README.md
DOC: Tweaks to comments in initdb.sh.
DEV: Split postgres example into separate db and hub containers.
DOC: Update the README for postgres example.
DOC: More tweaks to postgres example.
DOC: Add note about default username/password configuration.
s/bower/js/
drop support for old Python, IPython < 3

Require IPython >= 3.0, Python >= 3.3
DEV: Use docker links to set password environment variable in the hub.

Also, yell at people if they use the default password.
DOC: Fix typo in postgres example message.
DOC: Fix more typos in warning messages.
Merge pull request #87 from quantopian/postgres-example

Postgres example using docker
Merge pull request #89 from minrk/no-python-2

drop support for old Python, IPython < 3
update some file names

default config file is now `jupyterhub_config.py`,
to be consistent with everything else

add config files, runtime files to .gitignore