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, 26 insertions, 0 deletions

diff --git a/docs/dns.html b/docs/dns.html
index 56ce3ba..e8320e8 100644
--- a/docs/dns.html
+++ b/docs/dns.html
@@ -106,6 +106,32 @@ the  resolver.  In  case of error, the function returns <b><tt>nil</tt></b>
 followed by an error message.
 </p>
 
+<!-- getnameinfo ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
+
+<p class="name" id="getnameinfo">
+socket.dns.<b>getnameinfo(</b>[host] [, service]<b>)</b>
+</p>
+
+<p class="description">
+Resolves a host and/or a service name through the system resolver and
+returns their canonical name form. At least one of <tt>host</tt> or
+<tt>service</tt> must be given.
+</p>
+
+<p class="parameters">
+<tt>Host</tt> is an optional string with a host name or IP address.
+<tt>Service</tt> is an optional string with a service name or port number.
+</p>
+
+<p class="return">
+If <tt>host</tt> was given, returns a numerically-indexed table with the
+canonical host name found for each address the resolver returns for
+<tt>host</tt>. If <tt>service</tt> was also given, the canonical service
+name is returned as an additional value; if only <tt>service</tt> was
+given, its canonical name is returned by itself. In case of error, the
+function returns <b><tt>nil</tt></b> followed by an error message.
+</p>
+
 <!-- gethostname ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
 
 <p class="name" id="gethostname">