Add functions for busy waiting

[PatrickKa]

Description

If we only want to wait for a very short amount of time, then at some point suspending a thread and thereby performing a context switch, becomes less efficient than busy waiting. I would guess that up to a few or maybe a couple dozen microseconds we should busy wait. This matches with what Prof. Montenegro told me in an E-Mail. They did some measurements with an STM32F4 (I don't know the clock rate they used) and found that switch from a thread to an interrupt and back takes < 6 µs.