Hausdorff distance

This PR implements the Hausdorff distance. Docs, examples and tests are incomplete, but the functionality seems to be ok.

Some discussion has already taken place here: #738.

Ping @jni @JDWarner
if during the iteration over j, d2_j is found to be smaller than d2_max, then there is no need to compute the distance to the other points. Wouldn't this make the computation faster? Is there a standard algorithm to compute the hausdorff distance between two sets of points?