Plugin is even more fit for human consumption, but the code is growing
less and less fit (global variables, static gcode, the agony)
* Disable fan when reheating. Keeping the fan on the corner of the
priming tower made it detach from my bed and reheating is a little
faster without it off.
* Restore behavior of not reheating during a very short layer. If
layers end up short for both hotends, ooze returned and the effect of
the plugin was negated.
* Only hop z on the first layer to prevent a blob from forming at the
edge of the priming tower.