documentation: Update pids manual pages

Updated the full suite of manual pages for the procps_pids_*
functions. The only one missing is procps_pids_get which
may not be required.

doc/procps_pids_unref.3

@@ -0,0 +1,58 @@
+.\" (C) Copyright 2017 Craig Small <csmall@enc.com.au>
+.\"
+.\" %%%LICENSE_START(LGPL_2.1+)
+.\" This manual is free software; you can redistribute it and/or
+.\" modify it under the terms of the GNU Lesser General Public
+.\" License as published by the Free Software Foundation; either
+.\" version 2.1 of the License, or (at your option) any later version.
+.\"
+.\" This manual is distributed in the hope that it will be useful,
+.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
+.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+.\" Lesser General Public License for more details.
+.\"
+.\" You should have received a copy of the GNU Lesser General Public
+.\" License along with this library; if not, write to the Free Software
+.\" Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+.\" %%%LICENSE_END
+.\"
+.TH PROCPS_PIDS_UREF 3 2017-01-05 "libproc-2"
+.\" Please adjust this date whenever revising the manpage.
+.\"
+.SH NAME
+procps_pids_refg \-
+Clear memory of pids structure, if no longer used
+.SH SYNOPSIS
+.B #include <proc/procps.h>
+.sp
+.BI "int procps_pids_refg(struct pids_info **" info ");"
+.sp
+Link with \fI\-lprocps\fP.
+
+.SH DESCRIPTION
+.BR procps_pids_refg ()
+will note that one less reference is used for the specified structure. If
+this was the last reference, the function returns the memory for the
+PID information structure that was created with
+.BR procps_pids_new (3).
+
+.SH RETURN VALUE
+The function returns 0 if the structure was freed or a positive
+integer of the current references if there were others. It will
+return one of negative values below on failure.
+.TP
+.B -EINVAL
+One of the given parameters is incorrect.
+
+.SH VERSIONS
+.B procps_pids_refg()
+first appeared in libproc-2 version 0.0.
+
+.SH SEE ALSO
+.BR libproc (3),
+.BR procps_pids_new (3),
+.BR procps_pids_reap (3),
+.BR procps_pids_reset (3),
+.BR procps_pids_select (3),
+.BR procps_pids_sort (3),
+.BR proc (5).