Several documentation callbacks (doc/0 and mod_doc/0) are implemented
and `ejabberdctl man` command is added to generate a man page. Note
that the command requires a2x to be installed (which is a part of
asciidoc package).
Now every such string MUST be encapsulated into ?T() macro.
The macro itself is defined in include/translate.hrl.
Example:
-module(foo).
-export([bar/1]).
-include("translate.hrl").
bar(Lang) ->
translate:translate(Lang, ?T("baz")).
The callback is supposed to provide known options and their default
values, as long as the documentation. Passing default values into
get_mod functions is now deprecated: all defaults should be provided
by the Mod:mod_options/1 callback.
