Better debug logging for the parser

Remove the commented-out print statements, instead supply rosout debug messages.
That's a good point regarding warnings for common sentence types.

As for the spew, if we leave it as is, the user needs to turn on debug level before starting the driver up to see these messages, correct? I'd prefer to avoid spewing message to the terminal by default, but I'm okay with spewing them to rosout once the user has asked for debug level messages.

What I want to avoid is a situation where I can't tell why a message isn't being parsed because the debug message only got printed before I had my monitoring tools up and running.