docs: document socket.unix and socket.serial, fix stale/missing API referencesdocs/pre-release-audit

Pre-release documentation audit against master. Adds the two fully
undocumented modules and closes gaps found by diffing every docs/*.html
page against its corresponding source:

- New docs/unix.html and docs/serial.html (socket.unix stream/dgram and
  socket.serial were never documented), linked from index.html,
  introduction.html, socket.html and reference.html. serial.html notes
  the current lack of a baud/parity/flow-control API and includes an
  os.execute+stty workaround example. Both note Windows is unsupported.
- socket.html: document headers.setcanonic, point to unix/serial modules.
- tcp.html: document getfamily, setpeername/setsockname aliases.
- udp.html: document getfamily, getfd/setfd, dirty; document the
  ipv6-multicast-hops/ipv6-unicast-hops aliasing as current (known-buggy)
  behavior rather than the originally intended semantics.
- http.html: correct redirect text (301/302/303/307/308, was 301/302
  only); document MAXHEADERLINE/MAXHEADERSIZE.
- dns.html: document getnameinfo.
- ltn12.html: document source.rewind and BLOCKSIZE.
- installation.html: fix stale "LuaSocket 3.0" sample output to 3.1.0.
- reference.html: index every anchor added above plus new Unix/Serial
  blocks.

1 files changed, 29 insertions, 0 deletions

diff --git a/docs/socket.html b/docs/socket.html
index 570f6d5..de43135 100644
--- a/docs/socket.html
+++ b/docs/socket.html
@@ -51,6 +51,14 @@ To obtain the <tt>socket</tt> namespace, run:
 local socket = require("socket")
 </pre>
 
+<p>
+Two related transports are shipped as separate modules, loaded on demand
+with their own <tt>require</tt> call: <a href="unix.html">Unix domain
+sockets</a> (<tt>require("socket.unix")</tt>) and
+<a href="serial.html">serial ports</a> (<tt>require("socket.serial")</tt>).
+Both are only built on Unix-like platforms.
+</p>
+
 <!-- headers.canonic ++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
 
 <p class="name" id="headers.canonic">
@@ -94,6 +102,27 @@ local headers = require("socket.headers")
 headers.setcanonic("X-Request-ID")
 </pre>
 
+<!-- headers.setcanonic +++++++++++++++++++++++++++++++++++++++++++++++++ -->
+
+<p class="name" id="headers.setcanonic">
+socket.headers.<b>setcanonic(</b>name<b>)</b>
+</p>
+
+<p class="description">
+Registers a custom canonic capitalization for a header field name in
+<a href="#headers.canonic"><tt>socket.headers.canonic</tt></a>, for use
+when the automatic capitalize-first-letter-of-each-word rule would not
+reproduce it (e.g. an all-caps acronym).
+</p>
+
+<p class="parameters">
+<tt>Name</tt> is a string with the header field name in its desired
+canonic capitalization (e.g. <tt>"X-Request-ID"</tt>).
+</p>
+
+<p class="return">
+No return value.
+</p>
 
 <!-- bind ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->