fixed triangle -> vertices/indices processing, each edge holds a cache of indices (max of 4 that it can produce in any configuration) and vertices check this cache before adding their own - EdgeKey now just holds the interpolated vertex and an order-independent hash of the grid corners it is defined by - Lets us weld vertices within our own tolerance, roughly halves verts and allows smooth normals to be calculated properly (we lose hard edges a bit with this, but we can solve that procedurally later if we want)