Added in minimal way, ie did not convert ALL existing comment blocks to
bCNC format, as either existing seemed preferred, or already wored as
bCNC header blocks.
Enabling with --bcnc argument (not default) adds () gcode comment blocks
in bCNC format to provide colapsable blocks that can be dragged in bCNC
to edit or alows en/diable in the job.
41f036d84c