Refactor Filter Methods

[admtnnr]

Changed AbstractController::Callbacks to use define_method when creating before_filter, after_filter, etc. instead of class_eval.

[drogus]

Thanks for pull request, but class_eval is used here to not use blocks, which is better for performance. If you think that this will not have any impact you can try to prepare benchmark to ensure there is no regressions. Otherwise I don't think that this can be merged.