Better exception handling

Tighter PDP endpoint construction. (#11)

* Tighter PDP endpoint construction.

Can now handle a larger variety of input from the configuration.

Example: PDP_HOSTNAME can be localhost, or http://localhost,
or http://localhost/ and so on.

* Wrap all exceptions with AccessDeniedHttpException.

In the flow of control when it is confirmed that a controller
has the Authorize decorator, then after that point any exception
that occurs should result in authz denial.

* Use `docker build` in example README.

Saves the user some time and complexity because they don't have
to install dependencies on their machine.

* Update author email.