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.

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.

Adds in control of DRV8825 or A4988 interfaces stepper motors to the
timer infrastructure.  The interrupt handles acceleration and velocity
of stepper pulses including jerk (dA/dt) calculations, but it is up
to the user application to do path planning and generate S-curve
accelerations.  All stepper DIR pins are connected together, and then
the STEP from each stepper interface board is routed to an individual
pin.  For motions which involve multiple steppers, there is an option
to wait before beginning the next stepper motion until all active
steppers have completed their moves (i.e. moving to an X, Y where there
may be 1-2us delay between the X arrival and Y arrival).

A generic "startWaveform(pin, high-US, low-US, runtime-US)" and
"stopWaveform(pin)" allow for further types of interfaces.

Using a simple USB DSO shows that with only a single channel running,
a "tone(1000)" generates a waveform of 999.8Hz (500.1us per high/low).
Running additional generators or steppers will potentially increase the
jitter.

The implementation also is limited in the time of the shortest pulse
it can generate (mostly an issue for analogWrite at values <1% or
>99% of the scale).  Presently measurements of ~2-3us are seen on
the shortest of pulses.  There is no optimization to allow generating
two edges on a single interrupt, which leads to this minimum pulse
width.

The current implementation was written focusing on readability and
flexibility, not squeezing every cycle out of interrupt loops. There
are probably many places where the code could be optimized (after it's
fully validated!) to reduce CPU load and timing errors.

The closest time between interrupts is about 3us, so rework the waveform
generator to support phases down to 1us, while limiting the time in the
IRQ handler to avoid WDT or WiFi errors.

Waveforms now are based off of absolute cycle, not delta-cycles, and
the GPIOs are converted from a bit to a mask (to save clocks in the IRQ)
costing about 40 more bytes in global storage and reducing the minimum
period down from 3.5us to 1.20us at 160MHz.

Steppers still based off of delta-times.

Remove unneeded curTimeHigh/curTimeLow from the waveform structure,
saving 88 bytes (11 pins x 8bytes) of heap.  Also reduces inner loop
in the IRQ by an couple stores.

Also add measured offset to the waveform generation request, enabling
a 1/1000 reqest to produce a 1.083us high pulse, and a 999/1000 to
give a 1.083 low period, and the cycle time to be exactly 1.00ms over
the range.

IRQ doesn't need to be disabled on waveform changes as the code order
between the irq and start/stop is safe.

Allow GPIO16 as a stepper out pin

Remove the stepper code due to its size.  If it's included here it will
take a large amount of IRAM in *all* sketches, even those which do not
use it.

Add in a traditional callback option, which will allow Stepper to be put
in as a library, only being linked when necessary.

Allow tone to take a double/float as wekk as an integer frequency.
Set the pin to an output on a tone() call to match original code.