CaseFolded typedef
A nick or channel name folded under a server's casemapping.
Every map keyed by a nick or a channel is keyed by this type, so that a raw String can never be
used as an identity by accident.
The mapping that produced it is not stored. Two CaseFolded values are only comparable when they
came from the same connection, which is the only place they are ever used together.
Implementation
typedef CaseFolded = String;