Pointing to personal repositories for hacking
Sourcing the profile files which Heroku buildpacks set up for us (in /app/.profile.d), so that dependencies downloaded by the buildpack are available on PATH.

The docker run command which starts the app is now a little verbose so maybe should be refactored into a separate script; part of the verbosity is because of guarding against absence of the .profile.d directory.

This is to support use of the Java buildpack but has also been tested working for a simple Ruby web app.
Fixed broken ordering of steps when PORT is specified.
Allowing repository locations to be overridden with environment variables for hacking; using progrium's locations as the default.
Updating README to reflect Java buildpack and customizable repo URLs in bootstrap script.
Making repo location override variables shorter, simpler names for users.
Moving advanced installation section of README downwards for ease of reading for regular users.
Merge pull request #1 from rnorth/master

Prerequisite changes to allow Java buildpack support