Implement formula plumbing unit

[MassiveBattlebotsFan]

In draft until I can figure out why math_unit_flags hates my guts (occasional multi-driven net weirdness). Fixed.

Stuff that's changed:

• The FPU is enabled.
• divider32.vhdl is actually a divider.
• The latch system is more programmable.
• Every unit is now an adder, instead of half of them being subtractors.
• Input B can be inverted on a per-unit basis, to let every unit be a subtractor.
• The FPU halts when the next math cycle number is equal to the cycle compare register.
• Dividers can be configured to act as multipliers.

[MassiveBattlebotsFan]

This should be good to go now from a functionality perspective, although it definitely needs documentation.

[MassiveBattlebotsFan]

Hmm, it doesn't appear to fit on 100T platforms. Looking at optimizations to see if I can make it work.