MINOR: lua: allow socket api settimeout to accept integers, float, and doubles

Instead of hlua_socket_settimeout() accepting only integers, allow user
to specify float and double as well. Convert to milliseconds much like
cli_parse_set_timeout but also sanity check the value.

http://w3.impa.br/~diego/software/luasocket/tcp.html#settimeout

T. Fournier edit:

The main goal is to keep compatibility with the LuaSocket API. This
API only accept seconds, so using a float to specify milliseconds is
an acceptable way.

Update doc.
diff --git a/doc/lua-api/index.rst b/doc/lua-api/index.rst
index e7aa425..a83bbde 100644
--- a/doc/lua-api/index.rst
+++ b/doc/lua-api/index.rst
@@ -1906,12 +1906,13 @@
 
   The amount of time to wait is specified as the value parameter, in seconds.
 
-  The timeout modes are bot implemented, the only settable timeout is the
+  The timeout modes are not implemented, the only settable timeout is the
   inactivity time waiting for complete the internal buffer send or waiting for
   receive data.
 
   :param class_socket socket: Is the manipulated Socket.
-  :param integer value: The timeout value.
+  :param float value: The timeout value. Use flotting point to specify
+    milliseconds.
 
 .. _regex_class: