Add missing return statement.
Allow to set toolchain path, and catch no return value in non-void funcs.
Add double-include protection.
Define IrqHandler type.
Add TimerIrqDispatch class to regularize IRQ handling across MCUs.

So far, proof of concept implementation for MSP430.
They say __alway_inline__ would apply only to inline functions.
Add example for TimerIrqDispatch.