Fix custom converter reflection based initialization

[FabianTerhorst]

https://github.com/FabianTerhorst/FastLayout/blob/master/fastlayout-processor/src/main/java/io/fabianterhorst/fastlayout/processor/LayoutProcessor.java#L107 is throwing a exception every time.

[Alexander--]

I haven't had much time to read the code, but it looks like you are attempting to directly instantiate a class from annotated code (before it have been compiled). Naturally, this won't work (it is throwing something like MirroredTypeException, isn't it?)

Paperparcel have a neat, working implementation of pluggable converters: it searches for annotated classes like you do, then generates a code, which adds them to Map at runtime, somewhere during initialization of generated boilerplate. This allows you to retrieve user converters without reflection and use them at runtime by utilising polymorphism (they all inherit from specialized interface).