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, 54 insertions, 0 deletions

diff --git a/docs/man/nng_msg_header_chop.3.adoc b/docs/man/nng_msg_header_chop.3.adoc
new file mode 100644
index 00000000..78625365
--- /dev/null
+++ b/docs/man/nng_msg_header_chop.3.adoc
@@ -0,0 +1,54 @@
+= nng_msg_header_chop(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_chop, nng_msg_header_chop_u32 - remove data from end of message header
+
+== SYNOPSIS
+
+[source, c]
+----
+#include <nng/nng.h>
+
+int nng_msg_header_chop(nng_msg *msg, size_t size);
+
+int nng_msg_header_chop_u32(nng_msg *msg, uint32_t *val32);
+----
+
+== DESCRIPTION
+
+The `nng_msg_header_chop()` and `nng_msg_header_chop_u32()` functions remove
+data from the end of the header of message _msg_. 
+The first function removes _size_ bytes.
+The second function removes 4 bytes, and stores them in the value _val32_,
+after converting them from network-byte order (big-endian) to native
+byte order.
+
+== RETURN VALUES
+
+This function returns 0 on success, and non-zero otherwise.
+
+== ERRORS
+
+`NNG_EINVAL`:: The message header is too short to remove the requested data.
+
+== SEE ALSO
+
+<<nng_msg_alloc.3#,nng_msg_alloc(3)>>,
+<<nng_msg_header.3#,nng_msg_header(3)>>,
+<<nng_msg_header_append.3#,nng_msg_header_append(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)>>