exponential.c: Pass movement params on cmdline

Let the caller pass in accel, velocity and distance on the commandline
so we can plot different movements without recompiling.

Also, begin moving towards a velocity-plot array of slopes.
exponential: Add test cases and label plots
WIP: Use uint64_t integer math

We need to get down to 8-bit-efficient math without any FP math.
We lose too much precision with floats, so we have been using
doubles.  Let's start reigning that back in.

Convert the doubles back to floats.  To prevent the resulting
accumulated error, start using all integer math for step planning
during our piece-wise integration.  Calculate the overflow in a
remainder variable, and determine when to step the quotient by
comparing it to the divisor.

We will use 64-bit ints for now, and try to simplify that again
in a future commit.
Try to predict the next step in real-time

This fails because we always want to be called before our next step
so we can continue to integrate before we miss a step.  This is
fairly reliable for most reasonable values of A, V and DX, but it
requires far more interrupts than are truly necessary.  To fix that,
we will turn to the clock-based math method which is already used in
Teacup.
Integer math noise

This was attempted but failed.  Might want to try again later.
Here is some commented code.
Comment typo in master (cherry-pick me)
Move math into clock-based periodic update

Probably a bunch of other changes, but I forgot to push them separately.
Does it still work?
Refactor tracefile tools

These may be committed somewhere else, but I found them loose on this
branch, so I am committing them here.