Another Grid Library Except Terrible

This is a successor to my old crate cogs_gamedev's grids module. It adds opinionated integer-based coordinates and directions, along with some other useful things:

• Iterators over areas, edges of areas, and lines
• Grid<T>, which is like a HashMap<Coord, T> but faster

This crate is built alongside and for my W.I.P. roguelike Foxfire.