fixes #143 Protocols and transports should be "configurable"

This makes all the protocols and transports optional.  All
of them except ZeroTier are enabled by default, but you can
now disable them (remove from the build) with cmake options.

The test suite is modified so that tests still run as much
as they can, but skip over things caused by missing functionality
from the library (due to configuration).

Further, the constant definitions and prototypes for functions
that are specific to transports or protocols are moved into
appropriate headers, which should be included directly by
applications wishing to use these.

We have also added and improved documentation -- all of the
transports are documented, and several more man pages for
protocols have been added.  (Req/Rep and Surveyor are still
missing.)

1 files changed, 110 insertions, 0 deletions

diff --git a/docs/nng_ipc.adoc b/docs/nng_ipc.adoc
new file mode 100644
index 00000000..c5dac4f7
--- /dev/null
+++ b/docs/nng_ipc.adoc
@@ -0,0 +1,110 @@
+nng_ipc(7)
+==========
+:doctype: manpage
+:manmanual: nng
+:mansource: nng
+:icons: font
+:source-highlighter: pygments
+:copyright: Copyright 2017 Garrett D'Amore <garrett@damore.org> \
+            Copyright 2017 Capitar IT Group BV <info@capitar.com> \
+            This software 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_ipc - IPC transport for nng
+
+SYNOPSIS
+--------
+
+[source,c]
+----------
+#include <nng/transport/ipc/ipc.h>
+
+int nng_ipc_register(void);
+----------
+
+DESCRIPTION
+-----------
+
+The _nng_ipc_ transport provides communication support between
+_nng_ sockets within different processes on the same host. For POSIX
+platforms, this is implemented using UNIX domain sockets.  For Windows,
+this is implemented using Windows Named Pipes.  Other platforms may
+have different implementation strategies.
+
+// We need to insert a reference to the nanomsg RFC.
+
+Registration
+~~~~~~~~~~~~
+
+The _ipc_ transport is generally built-in to the _nng_ core, so
+no extra steps to use it should be necessary.
+
+URI Format
+~~~~~~~~~~
+
+This transport uses URIs using the scheme `ipc://`, followed by
+a path name in the file system where the socket or named pipe
+should be created.
+
+TIP: On Windows, all names are prefixed by `\.\pipe\` and do not
+occupy the normal file system.  On POSIX platforms, the path is
+taken literally, and is relative to the current directory, unless
+an extra leading `/` is provided.  For example, `ipc://myname` refers
+to the name `myname` in the current directory, whereas `ipc:///tmp/myname`
+refers to `myname` located in `/tmp`.
+
+The entire URI must be less than `NNG_MAXADDRLEN` bytes long.
+
+Socket Address
+~~~~~~~~~~~~~~
+
+When using an `nng_sockaddr` structure, the actual structure is of type
+`nng_sockaddr_ipc`.  This is a `struct` type with the following definition:
+
+[source,c]
+--------
+#define NNG_AF_IPC 2 <1>
+#define NNG_MAXADDRLEN 128
+
+typedef struct {
+    // ... <2>
+    uint16_t sa_family;                 // must be NNG_AF_IPC
+    char     sa_path[NNG_MAXADDRLEN];   // arbitrary "path"
+    // ...
+} nng_sockaddr_ipc;
+--------
+<1> The values of these macros may change, so applications
+should avoid depending upon their values and instead use them symbolically.
+<2> Other members may be present, but only those listed here
+are suitable for application use.
+
+The `sa_family` member will have the value `NNG_AF_IPC`.
+The `sa_path` member is an ASCIIZ string, and may contain any legal
+path name (platform-dependent), terminated by a `NUL` byte.
+
+Transport Options
+~~~~~~~~~~~~~~~~~
+
+The _ipc_ transport has no special
+options.footnote:[Options for security attributes and credentials are planned.]
+
+AUTHORS
+-------
+link:mailto:garrett@damore.org[Garrett D'Amore]
+
+SEE ALSO
+--------
+<<nng.adoc#,nng(7)>>
+
+COPYRIGHT
+---------
+
+Copyright 2017 mailto:garrett@damore.org[Garrett D'Amore] +
+Copyright 2017 mailto:info@capitar.com[Capitar IT Group BV]
+
+This document is supplied under the terms of the
+https://opensource.org/licenses/LICENSE.txt[MIT License].