9.3: removed legacy JELP commands ADDUMODE and ADDCMODE.
        added TS6::Base method ->register_ts6_command() for adding TS6 command handlers.
        added TS6 parameter modifier subroutines and message source lookup functions.
        renamed some outgoing command events to no longer use JELP command names.
        add modes to TS6 servers before sending out our burst.
        added TS6 outgoing commands BMASK (list mode burst) and TB (topic burst).
        added TS6 incoming command SJOIN (channel burst or creation).
        server method ->cmode_type() now returns -1 rather than undef when the mode doesn't exist.
        outgoing command callbacks now return a list of lines rather than an array reference.
        added TS6 utilities:
        obj_from_ts6:           convert a TS6 ID to an object;
        user_from_ts6:          convert a TS6 UID to a user object;
        server_from_ts:         convert a TS6 SID to a server object.