AxisStepper: implement stopStepping() and getSteppingState()
AxisSplitter: add TimerInstance typedef
implement AxisSharer and use it in aprinter.cpp
implement pausing
compile.sh: remove -lm
AvrPins: handle absence of pin change interrupts and provide a list of all ports
AvrPinWatcher: properly report errors for ports without pin change interrupts, and use use AvrPorts list to detect ports which do support them
AvrPinWatcher: fix ISRs as well
add NotFunc, needed by AvrPins
FixedPoint: add FixedResDivide
AvrPinWatcher: add PinWatcher alias
Implement a very simple 1-dimensional planner and homing using this.