Unsophisticated Avro transformers for `SpecificRecord` implementations.
* * Fix DSL Factory
- transformer was changed to `<? extends GenericContainer>`; change the DSL to match
* * Restore test log4j
* * Revert to supporting only SpecificRecord
* * Fix assert
* * Add multi-type deserialization with fluent API
* Polishing for PR comments
* * Remove type mappings; Exxpression now returns the type (or class name)
* Cache types created from class names
* Add type header in "toAvro" transformer
* * Remove the type cache (already handled by the class loader)
* * Don't convert the class to String in the "toAvro" transformer
9a2b75bae3