A series of bugfixes:
- use scientific notation in halmeter only when really necessary
- fix a position jump on stepper machines when reenabling after estop
- fix moving to [EMCIO]TOOL_CHANGE_POSITION during M6
detect and report to the user some realtime problems
(unexpected delays) that reflect a problem with the
hardware or realtime subsystem.
- fix step sometimes moving significantly past the end of a segment.
- fix bug where hitting step too quickly in a row could cause a resume.