Implemented FromIterator for std::hashmap
Implemented FromIterator for TrieMap and TrieSet
Stripped trailing spaces; Implemented FromIterator for TreeMap and PriorityQueue
auto merge of #7788 : MarkJr94/rust/from_iter, r=cmr

Added Iterators for HashMap/Set, TreeMap/Set, TrieMap/Set, and PriorityQueue as per Issue #7626