all: Drop RMAX software

This software was used only for one project, the mapping of Marscape
via the RMAX helicopter. Neither the RMAX hardware or Marscape exist
anymore. We still have the dataset file ... but if anyone was
interested, it could be processed with our generic PinholeSession.
stereo_mpi.in: Minor usage fix
Add Ben's sparse disparity Python code
sparse_disp: add --processes option