* due to server bugs, some offline buddies are still notified on publication,

  causing error reply, that pep accepts as event. check message type/presence of error tag.

* check input/output for validity, where applicable

* extract common code into one place

* add avatar

  * pep_avatar, avatar_cache, avatar, aavatar (separate)

    *       hook_avatar_metadata_in                               @ pep_avatar  

          | hook_avatar_need_data_in (or symbol-resolved request) @ avatar_cache  

          V hook_avatar_data_in                                   @ pep_avatar  

            hook_avatar_in                                        @ avatar_cache

    * (!!!) how to handle outgoing event? what and where should do what?

  * handle url avatars (curl)

  * report absence of avatar