Add a way to packetize incoming data even in the absence of a pending ORSSerialRequest.

[armadsen]

A common scenario for serial communications is a device that automatically sends packets of data periodically or in response to (real world) events, rather than as a response to some request from the computer. ORSSerialPort doesn't currently provide any help with parsing/packetizing this kind of incoming data, like it does for structured request/response scenarios.

It would be valuable to provide an API so that a user of ORSSerialPort could install a "packetizer", then be notified of incoming packets that have been validated. This could look quite similar to the existing response part of ORSSerialRequest support, including the use of a response evaluator block (could be called a "packet evaluator" block).

Some requirements for the API:

• Should not interfere with the existing raw data receipt mechanism (-serialPort:didReceiveData:).
• Should work simultaneously with the request response API.
• Should allow for multiple packetizers to be used at once, for cases where a serial device sends packets in more than one format.
• Should allow for removal of specific packetizers in order to cease notification for incoming packets of a given type.

I think this may warrant some refactoring of the existing request response API, so I think it should wait until the next major update (ie. 2.0).

[armadsen]

Implemented by pull request #66.