`util` module: Standard datatypes that shouldn't be in the global namespace

[cadebrown]

This module is for common and/or fundamental datatypes that should be in the standard library, but not a builtin name (to avoid clutter).

For example, types:

• util.Graph: General purpose graph, stored using sorted adjacency lists (or hash tables maybe). Needs to be a good general purpose graph datastructure, with directed edges. Edges and nodes should have a generic object val attribute
• util.Queue: General purpose double-ended-queue
• util.BST: Binary search tree, for sorted data collection, with range searches
• util.Bitset: Set of integers that can be stored efficiently, with a .asmask() function that returns an integer