add missing Nullable annotation
refactor StackedMap to StackedHashMap and implement LinkedList instead of Stack
refactor SetMap to HashSetMap
add timed collection interfaces, refactor collection names
refactor MultiValueMap to MultiValueBiMap
add removeValue(value) method
Use HashSetMap instead of MultiValueBiMap
add sub quests
Messenger accepts Object instead of Plugin for more versatility with chat prefix
add IChatPrefixed interface
fix PreCon.notNull for Nullable parameter, update comment
allow setting message prefixes