bin/35070: math(3) references section "3m", etc.

[David Schultz]

The math(3) manpage has undergone quite a bit of revision since
this PR was submitted, so I think all the original issues have
been taken care of.  Still to do (IMO):

- Move all the functions currently documented in ieee(3) to their
  own manpages.  The ieee(3) manpage is pretty cluttered, and
  it's hard to see the logical relationship between all the things
  that appear there.

- Move IEEE 754 details currently in math(3) to ieee(3).  Some of
  the material on exceptions probably belongs in fenv(3), and
  some of the material on representations belongs in float(3),
  which doesn't exist yet.