Add rules for `mod` and `rem`

[twadleigh]

...and possibly also for atan2 and hypot, if it is appropriate to move the special casing in ForwardDiff.jl for those functions to this package.

I will submit a PR shortly.

Of course, this would depend on resolving jrevels/RealInterface.jl#4 upstream.

[jrevels]

closed by #16