Keypoint index class

[lmmx]

N.B. — the keypoints.py module is only used by the optimise module

make_keypoint_index should clearly be a KeypointIndex class __init__ method, and project_keypoints should be a project method, removing the index passing as 2nd argument.

• This will probably extend to the inner function objective within optimise_params?

Additionally, draw_correspondences doesn’t belong in optimize, since it is called on the keypoint index and built on top of in the same way this should be another method of the KeypointIndex class, combined with debug_show.

• Since this is a debugging util, put it in debug_utils/keypoint_debug.py