Cosmetic simplification.
MotionPlanner: Cosmetic change.
MotionPlanner: Use the maximum metric instead of euclidean.

This only slightly changes how junctions are executed, the cartesian speed limit still works.
It seems this allows higher overall speeds.
TupleGet: Add TupleFindElem, fix const.
MotionPlanner: Optimization.
MotionPlanner: Optimization.
Enable runtime config and EEPROM on Melzi.
scripts/built-avr.sh: Make it possible to not disable erase.
Needed for direct programmers as opposed to bootloader.
MotionPlanner: Use FastEvent for callbacks.
MotionPlanner: Avoid a square root.
scripts/build-avr.sh: Built with -O3.
PrinterMain: Simplification, get rid of MoveBuildState.
LinearPlanner: Simplify junction speed limit.
Also fixes an unimportant bug about junction speed limit not being applied if there are lots of channel commands together.