Add anti-spam functionality for repeating messages #63
Description
DoS attacks by sending same messages multiple times in a short period from same or different user are becoming more common.
Same (or similar using fuzzy search??) message (from same or different users) in same channel three or more times (setting) per 30s (setting) should be filtered.
Also add Ops option to kick-ban those users ($mask type 2 (identical host/ip) or dropdown setting) for specified no. of minutes (setting) and optionally to apologise to channel (setting) - random delay of up to 20x 1/10s and cancel if banned by someone else first. Also report action in Ops chat if enabled.