Remove and rewrite all the parts of the core/libraries using TIMER1
and consolidate into a single, shared waveform generation interrupt
structure. Tone, analogWrite(), Servo all now just call into this
shared resource to perform their tasks so are all compatible
and can be used simultaneously.
This setup enables multiple tones, analogWrites, servos, and stepper
motors to be controlled with reasonable accuracy. It uses both TIMER1
and the internal ESP cycle counter to handle timing of waveform edges.
TIMER1 is used in non-reload mode and only edges cause interrupts. The
interrupt is started and stopped as required, minimizing overhead when
these features are not being used.
A generic "startWaveform(pin, high-US, low-US, runtime-US)" and
"stopWaveform(pin)" allow for further types of interfaces. Minimum
high or low period is ~1 us.
Add a tone(float) method, useful when working with lower frequencies.
Fixes#4321. Fixes 4349.
