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, 137 insertions, 0 deletions

diff --git a/docs/nng_tcp.adoc b/docs/nng_tcp.adoc
new file mode 100644
index 00000000..a1d0cdab
--- /dev/null
+++ b/docs/nng_tcp.adoc
@@ -0,0 +1,137 @@
+nng_tcp(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_tcp - TCP/IP transport for nng
+
+SYNOPSIS
+--------
+
+[source,c]
+----------
+#include <nng/transport/tcp/tcp.h>
+
+int nng_tcp_register(void);
+----------
+
+DESCRIPTION
+-----------
+
+The _nng_tcp_ transport provides communication support between
+_nng_ sockets across a TCP/IP network.  Both IPv4 and IPv6
+are supported when the underlying platform also supports it.
+
+// We need to insert a reference to the nanomsg RFC.
+
+Registration
+~~~~~~~~~~~~
+
+The _tcp_ 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 `tcp://`, followed by
+an IP address or hostname, followed by a colon and finally a
+TCP port number.  For example, to contact port 80 on the localhost
+either of the following URIs could be used: `tcp://127.0.0.1:80` or
+`tcp://localhost:80`.
+
+When specifying IPv6 addresses, the address must be enclosed in
+square brackets (`[]`) to avoid confusion with the final colon
+separating the port.
+
+For example, the same port 80 on the IPv6 loopback address ('::1') would
+be specified as `tcp://[::1]:80`.
+
+NOTE: When using symbolic names, the name is resolved when the
+name is first used. _nng_ won't become aware of changes in the
+name resolution until restart,
+usually.footnote:[This is a bug and will likely be fixed in the future.]
+
+The special value of 0 (`INADDR_ANY`) can be used for a listener
+to indicate that it should listen on all interfaces on the host.
+A short-hand for this form is to either omit the address, or specify
+the asterisk (`*`) character.  For example, the following three
+URIs are all equivalent, and could be used to listen to port 9999
+on the host:
+
+  1. `tcp://0.0.0.0:9999`
+  2. `tcp://*:9999`
+  3. `tcp://:9999`
+
+The entire URI must be less than `NNG_MAXADDRLEN` bytes long.
+
+Socket Address
+~~~~~~~~~~~~~~
+
+When using an `nng_sockaddr` structure, the actual structure is either
+of type `nng_sockaddr_in` (for IPv4) or `nng_sockaddr_in6` (for IPv6).
+These are `struct` types with the following definitions:
+
+[source,c]
+--------
+#define NNG_AF_INET    3 <1>
+#define NNG_AF_INET6   4
+#define NNG_MAXADDRLEN 128
+
+typedef struct {
+    // ... <2>
+    uint16_t sa_family;                 // must be NNG_AF_INET
+    uint16_t sa_port;                   // TCP port number
+    uint32_t sa_addr;
+    // ...
+} nng_sockaddr_in;
+
+typedef struct {
+    // ... <2>
+    uint16_t sa_family;                 // must be NNG_AF_INET6
+    uint16_t sa_port;                   // TCP port number
+    uint8_t  sa_addr[16];
+    // ...
+} nng_sockaddr_in6;
+--------
+<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_INET` or `NNG_AF_INET6`.
+The `sa_port` and `sa_addr` are the TCP port number and address, both in
+network byte order (most significant byte is first).
+
+Transport Options
+~~~~~~~~~~~~~~~~~
+
+The _tcp_ transport has no special
+options.footnote:[Options for TCP keepalive, linger, and nodelay 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].