extend current classloader instead of creating a classloader chain.
#103 keep defined accessibility modifier of mapper and mapping methods in the generated code
#103 Formatting, added a todo
#120 refactoring first attempt after feedback. Making a clean overview by squashing earlier commits on 120. Rebasing master.
#120 reintroducing lost generics selection check and making sure  MapperCreationProcessor state is cleared.
#120, solving cyclic packaging dependencies, Moved Context (as inner class) to ConversionContext in model.common, corrected BuildIn to BuiltIn, all requested built-in methods added
#120 Method and BuiltInMethod implement a common interface that can be used for matching.
#120 Moving BuildInMethod to the source model
#120 Renaming Method to SourceMethod
#120 Renaming BasicMethod to Method
#120 Propagate built-in methods as MappingMethod implementation to the Mapper in order to avoid the need for specific handling in the template
#120 Formatting and commenting
#120 Making built-in methods null-safe
#120 Moving built-in methods to o.m.a.model.source.builtin
#120 Don't hold a reference to TypeFactory in built-in method types
#120 Minor doc improvements
#120 Consolidating method reference look-up in MapperCreationProcessor
#120 Removing unused constructor
#128 Adding support for enum mapping methods
#128 Raising an error in case an enum constant is mapped more than once