manager: add ~rehash
events/player: minor tidy up, use inheritance instead of attributes for setup()
properties: output format strings to rebuild death messages
manager: change PlayerDeath dispatching

use one ServerOutput listener instead of one per death:
- at most one death event dispatched per actual death
- we give the PlayerDeath event a format string instead of a raw line
events/player: generate text from the format attribute
plugins/irc: mangle usernames in death messages. fix #51