math.3 revisions

[David Schultz]

Our current math.3 has a number of problems, largely, I think,
because it needs so much work that it scares people away.  In
particular:

- It is still written in man(7) format instead of mdoc(7) format.

- It is largely dedicated to VAX floating-point.

- It describes the old (pre-1994) UCB math library whence it
  came, rather than the new FDLIBM library that we have now.

- Its list of functions is inaccurate and incomplete.

I've gone ahead and fixed these problems and made updates where I
could.  The result is mostly correct and halfway up-to-date,
although it still has some remnants of man(7) markup, and
generally needs a lot more work.  (Entire sections could probably
stand to be moved, added, etc., but it currently compiles and looks right.)

The diff is at
	http://people.freebsd.org/~das/patches/math.3.diff
but you may find it easier to look at the new file because the changes
are so extensive:
	http://people.freebsd.org/~das/patches/math.3

My questions are:

- Does anyone object to any parts of this change?

- Where do we go from here?  Do I commit this as is and refine it
  more over time, or does someone with more mdoc-fu than me want to
  hack on it some more first?