Added call method to the container.

Ok as promised here's the second pull request for the container class. 100% backwards compatible and tested.

The new call method allows you to execute a callable and inject its dependencies using the container.

I have a third pull request that I'm working on but its a bit bigger so I'll probably wait until tomorrow since its getting pretty late here. I have a working prototype but I want to go through the code and write some more tests for it.

What I'm working on is making the route dispatcher execute the action using the ```Container::call``` method. This will enable us to inject dependencies directly into the rote controller methods and/or closures. We're converting some Silex applications to Mako and its a pretty useful feature that they have.

It would also be nice to do the same for task actions and possibly migrations as well.