Initial implementation of abstract mappers
Updated 'isAbstract' to 'favorsExtension'; mappers that 'favorExtension'
can still be used if the types match exactly
Added 'favorsExtension' as a globally configurable property on
DefaultMapperFactory.Builder.
Added FavorsExtensionTestCase
Added ability to flush the strategy cache when a mapper is registered
after the factory has already been built.
Added multi-level test
Added test for possibility of duplicate mappers in 'usedMappers'
hierarchy, and a fix in initializeUsedMappers to avoid this possibility
Merge pull request #31 from orika-mapper/abstract-mappers

Abstract mappers ('favorExtension')