Implement plane-to-plane transformations for tangent plane projections

It could be useful to implement an alternative ``pixel_to_pixel`` which implements the fast reprojection algorithm mentioned here:

http://montage.ipac.caltech.edu/docs/algorithms.html

specifically for WCSes with the same coordinate frame and in a specific subset of projections, it should be possible to do much faster computations of pixel-to-pixel transformations.

Start at the existing pixel_to_pixel entry point and read the linked Montage reprojection algorithms. Determine which same-coordinate-frame projections can use the proposed plane-to-plane path, then define and validate the supported fast transformations; the issue does not name specific files or tests.

Written by the indexing model from the issue text.