Configuration system refactor: documentation

Update the documentation according to the new Propel2 configuration system.
See pull request 527 on Propel2 repository https://github.com/propelorm/Propel2/pull/527

*Note*: I've added a new layout ("configuration") which is the same as "documentation", with a jquery-ui tabbed panel, to show the various formats of the configuration file.
Maybe you can put a "the" before the function name. Also I think it's "inspired of", not "inspired on" and you should s/"In example"/"For example/instance" :-p