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, 7 insertions, 2 deletions

diff --git a/docs/http.html b/docs/http.html
index c6423ba..316cd2e 100644
--- a/docs/http.html
+++ b/docs/http.html
@@ -114,7 +114,11 @@ the HTTP module:
 <ul>
 <li> <tt>PROXY</tt>: default proxy used for connections;</li>
 <li> <tt>TIMEOUT</tt>: sets the timeout for all I/O operations;</li>
-<li> <tt>USERAGENT</tt>: default user agent reported to server.</li>
+<li> <tt>USERAGENT</tt>: default user agent reported to server;</li>
+<li> <tt>MAXHEADERLINE</tt>: maximum length, in bytes, of a single response
+header line. Defaults to 8192;</li>
+<li> <tt>MAXHEADERSIZE</tt>: maximum total size, in bytes, of all response
+header lines combined. Defaults to 65536.</li>
 </ul>
 
 <p class="note">
@@ -183,7 +187,8 @@ pump step function used to move data.
 Defaults to the LTN12 <tt>pump.step</tt> function.</li>
 <li><tt>proxy</tt>: The URL of a proxy server to use. Defaults to no proxy;</li>
 <li><tt>redirect</tt>: Set to <tt><b>false</b></tt> to prevent the
-function from  automatically following 301 or 302 server redirect messages;</li>
+function from automatically following 301, 302, 303, 307 or 308 server
+redirect messages;</li>
 <li><tt>create</tt>: An optional function to be used instead of
 <a href="tcp.html#socket.tcp"><tt>socket.tcp</tt></a> when the communications socket is created.</li>
 <li><tt>maxredirects</tt>: An optional number specifying the maximum number of