Stream JSON serialization

[nstdio]

Original issue: FasterXML/jackson-databind#3010

[nstdio]

@cowtowncoder Essentially original question was: Is there a way to stream JSON serialization in a convenient way for user to consume. In other words, for deserialization we have MappingIterator which lazily parses the input and binds it to the POJO's, do we have same kind of feature for serialization?

[cowtowncoder]

@nstdio For serialization existing target choices are:

1. Blocking I/O (stream) -- OutputStream, Writer -- as well as secondary convenience type(s) (File)
2. Static content -- byte[], char[], String
3. ByteBuffer (although just a simple wrapper to adopt via OutputStream)

and question then is what else could/should be added, and where.

[nstdio]

I believe this could possibly have relation to #45