Fix some lint.

Too much or too little whitespace;
improve macro usage;
add missing .El;
merge error sections for same error code.

Refer to init_routine in the DESCRIPTION section with .Fa instead of .Fn

Use

.Vt type var No = Dv INITIALIZER;

to provide examples of static initialization in SYNOPSIS section.
.Va macro does the wrong thing (check groff PostScript output) and the
need for .Pp kludge (now dropped) should have been an indication too.

While here move static initialization example to be right after the
declaration of *_init().

branches: 1.7.6; 1.7.12;
Update conformance to the 2001 revision.

Use similar markup than in pthread_mutex_init(3) etc. with the initializer
macro. Improve wording slightly.

.Dv.

Use .In instead of .Ar Pa

branches: 1.3.8;
Move TNF licenses to 2 clause form

branches: 1.2.32;
$NetBSD$, not $Header$.

Man pages for libpthread, adapted from FreeBSD by Stephen Degler.