fixes #286 nng_pair0_open (and all others) need man page

fixes #279 consider restructuring man sections

This represents a rather significant rework, and major editing
effort, for the entire set of manual pages.

All of the pages now have a section number in their filename;
this assists in some other tooling, particularly ebook generation
as every link needs to be programmatically modified when combined
into an ebook.

Section 5 is introduced, and populated with pages for the main
types, and all options are now documented.

Numerous errors have been corrected, including rewriting certain
portions such as the header section of the surveyor protocol.

Much work has been done to facilitate index generation, although
certainly more work remains here.

Every internal link within these pages now resolves; there are no
more dead links.  (This is required to generate Kindle format books.)

1 files changed, 55 insertions, 0 deletions

diff --git a/docs/man/nng_msg_header_append.3.adoc b/docs/man/nng_msg_header_append.3.adoc
new file mode 100644
index 00000000..922f22b5
--- /dev/null
+++ b/docs/man/nng_msg_header_append.3.adoc
@@ -0,0 +1,55 @@
+= nng_msg_header_append(3)
+//
+// Copyright 2018 Staysail Systems, Inc. <info@staysail.tech>
+// Copyright 2018 Capitar IT Group BV <info@capitar.com>
+//
+// This document is supplied under the terms of the MIT License, a
+// copy of which should be located in the distribution where this
+// file was obtained (LICENSE.txt).  A copy of the license may also be
+// found online at https://opensource.org/licenses/MIT.
+//
+
+== NAME
+
+nng_msg_header_append, nng_msg_header_append_u32 - append to message header
+
+== SYNOPSIS
+
+[source, c]
+----
+#include <nng/nng.h>
+
+int nng_msg_header_append(nng_msg *msg, const void *val, size_t size);
+
+int nng_msg_header_append_u32(nng_msg *msg, uint32_t val32);
+----
+
+== DESCRIPTION
+
+The `nng_msg_header_append()` and `nng_msg_header_append_u32()`
+functions append data to
+the end of the headers of message _msg_, reallocating it if necessary.
+The first function appends _size_ bytes, copying them from _val_.
+The second function appends the value _val32_ in network-byte order
+(big-endian).
+
+
+== RETURN VALUES
+
+This function returns 0 on success, and non-zero otherwise.
+
+== ERRORS
+
+`NNG_ENOMEM`:: Insufficient free memory exists.
+
+== SEE ALSO
+
+<<nng_msg_alloc.3#,nng_msg_alloc(3)>>,
+<<nng_msg_header.3#,nng_msg_header(3)>>,
+<<nng_msg_header_chop.3#,nng_msg_header_chop(3)>>,
+<<nng_msg_header_insert.3#,nng_msg_header_insert(3)>>,
+<<nng_msg_header_len.3#,nng_msg_header_len(3)>>,
+<<nng_msg_header_trim.3#,nng_msg_header_trim(3)>>,
+<<nng_msg_free.3#,nng_msg_free(3)>>,
+<<nng_strerror.3#,nng_strerror(3)>>,
+<<nng.7#,nng(7)>>