Implement the Jonker-Volgenant assignment algorithm

This implementation is based on the Pascal code provided by Jonker and
Volgenant themselves in their paper:

	Jonker, R., & Volgenant, A. (1987). A shortest augmenting
	path algorithm for dense and sparse linear assignment problems.
	Computing, 38(4), 325-340

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Add a test for the Jonker-Volgenant algorithm

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>