Introducing transformation logic.

This introduces interfaces and some experimental implementations
for import and export transformers.
Introducing transformation logic.

This introduces interfaces and some experimental implementations
for import and export transformers.
Top level import test script
Merge branch 'IntroducingTransformers' of github.com:creative-work-metadata/creative-work-metadata into IntroducingTransformers
Merge branch 'IntroducingTransformers'
Fix default value of Work::$types