core: add container::{MutableMap, MutableSet}
std: Code cleanup in treemap
std: TreeMapIterator::next should probaby use "&mut self" but hit's a bug
std: fix treemap.rs test
Add container::{ImmutableMap,ImmutableSet}
wip: modernize fun_treemap to use containers
wip
wip: more fun
wip fun
squash fun
squash fun