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.

PDP input bug fix

v7.4.3

Add host platform specific instructions to README.

Better exception handling

v7.4.2

Update author email.

Update example for PHP 7.4

v7.4.1

Update example app to use middleware v7.4 (#7)

Support PHP 7.4.*

Earlier implementation worked only with PHP 8+

OPA middleware built for Symfony using PHP 8

v8.0.0

Add README for example app. (#5)