Generate ejabberd.yml.5 man page from source code directly

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).

src/ejabberd_admin.erl

@@ -388,7 +388,11 @@ get_commands_spec() ->
      #ejabberd_commands{name = gc, tags = [server],
 			desc = "Force full garbage collection",
 			module = ?MODULE, function = gc,
-			args = [], result = {res, rescode}}
+			args = [], result = {res, rescode}},
+     #ejabberd_commands{name = man, tags = [documentation],
+                        desc = "Generate Unix manpage for current ejabberd version",
+                        module = ejabberd_doc, function = man,
+                        args = [], result = {res, restuple}}
     ].
 
 

src/ejabberd_config.erl

@@ -36,6 +36,7 @@
 -export([default_db/2, default_db/3, default_ram_db/2, default_ram_db/3]).
 -export([beams/1, validators/1, globals/0, may_hide_data/1]).
 -export([dump/0, dump/1, convert_to_yaml/1, convert_to_yaml/2]).
+-export([callback_modules/1]).
 
 %% Deprecated functions
 -export([get_option/2, set_option/2]).
@@ -63,6 +64,7 @@
 -callback opt_type(atom()) -> econf:validator().
 -callback options() -> [atom() | {atom(), term()}].
 -callback globals() -> [atom()].
+-callback doc() -> any().
 
 -optional_callbacks([globals/0]).