0.4.0

This is nearly 1.0 ready, but I would like to see some additional
changes in the following areas:

* Option refactoring. We have a huge number of options now.
* Extensibility. It should be easier to extend/inherit from
  Heroku::Bouncer to tweak its behavior. This was possible under 0.3.x
  but is no longer true in 0.4.0.
* Remove backwards compatibility support (i.e. ENV vars)

To those upgrading, please note that a great deal has changed. Backwards
compatibility with warnings has been maintained in this version, but not
throughly tested. Extensibility has not - you'll need to do some new
tricks if you have extended Heroku::Bouncer in your app.