Add "info processor" command to CLI debugger

We should add a new "info processor" command to the CLI debugger, which would print out either the parser or unparser depending on which is available.

This would likely replace the InfoProcessorBase abstract class with a concrete InfoProcessor object. And then the "not available" logic would move to the individual parser/unparse commands. E.g.

class InfoParser ... {
  def act(...) = {
    state match {
      case _: PState => debugPrintln("%s: %s".format(name, processor.toBriefXML(2)))
      case _ => debugPrintln("%s: not available".format(name))
    }
  }
}

InfoUnparser would be the same but would match on UState instead of PState.