Feature/json file config

File config as requested in https://github.com/EventStore/EventStore/issues/255

RFC to some extent. Still left to do: the reflection pieces of https://github.com/logary/logary/compare/feature/json-file-config?expand=1#diff-3813c1de9f72fe80a957a22142c76680R18 which dead with instantiating a target from a name.