replace ConstVector trait with the Container trait
implement Mutable trait for vec
remove remaining is_not_empty functions/methods
use mutable function argument syntax in treemap
use mut function argument syntax in priority_queue
Merge pull request #4633 from thestinger/treemap

use mutable function argument syntax in treemap/priority_queue
Merge pull request #4625 from thestinger/container

more little container improvements
doc typo