Provide JSON Reader/Writer generator relying on Jackson Streaming APIs

Current pull request proposes the addition of JSON Reader/Writer generation; generated classes rely on Jackson Streaming APIs defined in com.fasterxml.jackson.core:jackson-core:2.X.X artifact.

An IT compliant with Modello best practice is missing, I just tested it taking the maven.mdo from SVN, dropping the DOM fields, then reading a pom.xml, generated the JSONized version, then read back and check the Model.

Please note that exploded Map/Properties are not yet supported in the reader, while the writer is able already to serialize them...

I hope you will appreciate the initial effort and bring it to a higher level!

Best,
-Simo