Make transformer type parameters more concrete to let users control types.
Merge pull request #33 from yjbanov/master

Make transformer type parameters more concrete to let users control type...
Tiny but significant syntax fixes in EmptyEntity
Fix parameter order in ProxyException
Fix library names
Fix type annotations in emitter
Add missing addAll implementation in LocalDataMap
Added unimplementations of abstract methods in _ErrorEntity
Make concrete RequestHandler implementations extend rather than implement.
API to create a request handler from functions/closures.
Merge pull request #34 from yjbanov/master

A bunch of unrelated fixits (see individual commits)