SGM: reindent #22
SGM: simplify the linear assignment problem #22

It will be sparsish, if the graph is sparse.
This gives us a 30% speedup.
SGM: use sparse matrices, except for solve_LSAP #22

This makes things 3-4 times faster.
SGM: eliminate some matrix multiplications for speedup #22
Col and row minimum of sparse matrices.
Row and column maximum for sparse matrices.
Minimum in which row/col in sparse matrices
SGM: add C LSAP implementation from clue package
Merge branch 'feature-sgm' into develop