misc: Rename (Episode).(Inc|Dec) to (Episode).(IncPart|DecPart)
misc: Add an iterator to EpisodeRange
misc: Make the iterator part of EpisodeContainer interface

Also adds iterators to Episode (returns a single copy of itself) and to
EpisodeList (returns the contents of the iterators of each sublist in
sequence).
misc: (*EpisodeList).Sub: allow subtracting arbitrary containers
misc: Make String() and Format() not pointer methods
anidb: Implement USER
anidb: Parse the LID from FILE response

Each file has a different LID (or none) depending on the currently logged
in user. LID are globally unique.
anidb: Implement MYLIST for single files