#108 Iterable and ArrayMapping alignment

This PR is for a large part based on the work of @gunnarmorling .

I've added on the functionality level:
1. handling of `@NullValueMapping`
2. `void` return types.
3. handling target via `@TargetMapping`
4. beautified the array copy so that a conversion / mapping-method is called only once (not also for .length).
5. forging methods automatically

Extensive unit test (also on conversion)