intro(3M) => math(3M), move see also's to end

intro(3M) => math(3M), move see also's to end

SCCS-vsn: lib/libm/common_source/asinh.3 6.2
SCCS-vsn: lib/libm/common_source/erf.3 6.2
SCCS-vsn: lib/libc/stdlib/exit.3 6.2
SCCS-vsn: lib/libm/common_source/exp.3 6.8
SCCS-vsn: lib/libm/common_source/floor.3 6.4
SCCS-vsn: lib/libm/common_source/hypot.3 6.5
SCCS-vsn: lib/libm/common_source/ieee.3 6.2
SCCS-vsn: lib/libm/common_source/infnan.3 6.3
SCCS-vsn: share/man/man3/intro.3 6.5
SCCS-vsn: lib/libm/common_source/j0.3 6.6
SCCS-vsn: lib/libm/common_source/lgamma.3 6.2
SCCS-vsn: lib/libm/common_source/sin.3 6.6
SCCS-vsn: lib/libm/common_source/sinh.3 6.5
SCCS-vsn: lib/libm/common_source/sqrt.3 6.2