floating point stuff in std.math

[Berni44]

We are currently at splitting std.math into sub modules [1]. 
There the question arose, how to handle the floating point stuff, 
that's in there: Functions like feqrel, nextDown, isClose but 
also IeeeFlags and FloatingPointControl.

Some ideas:

a) IeeeFlags and FloatingPointControl goes into std.math.hardware 
and all else into std.math.floats.

b) The same, but std.math.floats is split into two modules, e.g. 
std.math.comparison (feqrel, isClose, ...) and 
std.math.floatmanip (nextDown, ilogb, ...)

c) Moving everything out of std.math and into it's own module, 
e.g. std.floats.

Any opinions or ideas on this?

[1] https://github.com/dlang/phobos/pull/7924