Refactored Config and ConfigInterface

**Note**: According to [SO](http://stackoverflow.com/questions/10081053/how-to-change-the-base-branch-of-a-pull-request) it is not possible anymore to change the target branch of a pull-request. I'll just reopen it. The old one can be found here: https://github.com/wsdl2phpgenerator/wsdl2phpgenerator/pull/99.

* [x] Refactor the Config class and its interface to use `OptionsResolver`
* [x] Fix tests
* [x] Add test for `allowedValues` and `normalizers` in the config class.
* [x] Update documentation.
* [x] Add doc blocks for the new methods. ~~Sorry, no IDE on my side~~.

Well. This is a first shot to tackle issue https://github.com/wsdl2phpgenerator/wsdl2phpgenerator/issues/94. This definitely needs review, because after changing the config class and the interface, I just fixed the tests to work again and I must admit that some parts of the code are still a black box to me.