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.
The changes are very similar to those from previous commit:
* Now there is no need to pass validating function in
gen_mod:get_opt() and gen_mod:get_module_opt() functions,
because the modules' configuration keeps already validated values.
* New functions gen_mod:get_opt/2 and gen_mod:get_module_opt/3 are
introduced.
* Functions gen_mod:get_opt/4 and get_module_opt/5 are deprecated.
If the functions are still called, the "function" argument is
simply ignored.
* Validating callback Mod:listen_opt_type/1 is introduced to validate
listening options at startup.
Now 'From' and 'To' arguments must be omitted in functions
and structures related to routing.
The commit deprecates the following functions:
ejabberd_router:route/3 in favor of ejabberd_router:route/1
ejabberd_router:route_error/4 in favor of ejabberd_router:route_error/2
ejabberd_local:route_iq/4 in favor of ejabberd_local:route_iq/2
ejabberd_local:route_iq/5 in favor of ejabberd_local:route_iq/3
The format of {route, From, To, Packet} is changed in favor of {route, Packet}
