Remove experimental support for avro schemas

 - Feature set for events is too different from REST services
 - In particular, event systems need streaming and union types
 - Remove avro support for now as it is too experimental to be
   of any use.
Merge pull request #157 from gilt/avro

Remove experimental support for avro schemas


  - Feature set for events is too different from REST services
  - In particular, event systems need streaming and union types
  - Remove avro support for now as it is too experimental to be of any use.