Document long double versions of these routines.

Convert to mdoc and fix stuff while here.

Add manpages for the complex math functions, originally from SUSv3,
roff source from the Linux documentation project.
Modifications before import:
-added NetBSD RCS ID
-removed Linux PROLOG and decla

Add manpages for the complex math functions, originally from SUSv3,
roff source from the Linux documentation project.
Modifications before import:
-added NetBSD RCS ID
-removed Linux PROLOG and declarations with "long double"
-ran the "deshallify" script as required by The Open Group
Split out complex related things into an own Makefile fragment.
Thanks to hubertf for directions.

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