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, 63 insertions, 0 deletions

diff --git a/docs/man/nng_http_req_add_header.3http.adoc b/docs/man/nng_http_req_add_header.3http.adoc
new file mode 100644
index 00000000..d47e112e
--- /dev/null
+++ b/docs/man/nng_http_req_add_header.3http.adoc
@@ -0,0 +1,63 @@
+= nng_http_req_add_header(3http)
+//
+// 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_http_req_add_header - add HTTP request header
+
+== SYNOPSIS
+
+[source, c]
+----
+#include <nng/nng.h>
+#include <nng/supplemental/http/http.h>
+
+int nng_http_req_add_header(nng_http_req *req, const char *key,
+    const char *val);
+----
+
+== DESCRIPTION
+
+The `nng_http_req_add_header()` adds an HTTP header for the request
+_req_ and the _key_ to the _val_.  The _key_ and _val_ are copied.
+
+If a header with the value of _key_ already exists, then a comma
+and whitespace separate are appended to it, followed by _val_.
+
+If no such header already exists, then one is created with the value _val_.
+
+TIP: The HTTP specification requires that duplicate headers be treated
+identically to a single header with multiple comma-delimited values.
+
+TIP: See <<nng_http_req_set_header.3http#,`nng_http_req_set_header()`>> if
+replacement of an existing header rather than appending to it is desired.
+
+The value of _key_ is case insensitive, and should not include the final
+colon in an HTTP header.
+For example, specifying `Host` or `hOSt` are
+equivalent, whereas the value `Host:` is not a legal header key.
+
+== RETURN VALUES
+
+This function returns 0 on success, and non-zero otherwise.
+
+== ERRORS
+
+`NNG_ENOMEM`:: Insufficient memory to perform the operation.
+`NNG_ENOTSUP`:: No support for HTTP in the library.
+
+== SEE ALSO
+
+<<nng_http_req_alloc.3http#,nng_http_req_alloc(3http)>>,
+<<nng_http_req_del_header.3http#,nng_http_req_del_header(3http)>>,
+<<nng_http_req_get_header.3http#,nng_http_req_get_header(3http)>>,
+<<nng_http_req_set_header.3http#,nng_http_req_set_header(3http)>>,
+<<nng.7#,nng(7)>>