bipartite cardinality matching

[Wikunia]

Maybe can be faster with an implementation of the Hopcroft Karp algorithm but read that this is normally not faster than the basic BFS implementation.
If this looks good I'll of course add it to the README.

Additionally:

• There is probably a faster implementation for unsorted ei
• Needs implementation for a sparse matrix as bipartite matching has it
• Remove the m <= n constraint

[dgleich]

I'm behind on things, but we'll take a look at this soon!