That way we can take advantage of printer pipelining within a job
even when fast_return is turned off.
This refactoring was also necessary for further changes in how
fast_return will work.
* Job query, canceling
* Printer status for idle/completion detection
* Many fixes
* Head temperature
Todo:
* Report printer status in human readable
* Better job queries
* Decode sensor data & report (know how to report temperature)
* 8x12 media handling/reporting