FlatLatticeTiling: record increment vectors with unit diagonal, and over tiled dimensions

- The 'eye_increment' matrix is n x n, with unit diagonal on non-tiled dimensions
- The 'tiled_increment' matrix is tn x tn, with tn the number of tiled dimensions
- These will be used to transform from normalised coordinates to/from generating integers
FlatLatticeTiling: store padding in lower/upper bound vectors

- added in FLT_GetBounds() if padding vector is non-NULL