Support for unweighted kNN graphs

[stanleyjs]

I'm wondering if the output of G = graphtools.Graph(X,decay=None) is working as intended. My impression was that with decay=None, a kNN graph would be created. However, inspection of G.K reveals that the kernel matrix is still weighted - some edge weights are 1, other 0.5. Is this the intended behavior? It probably arises from the symmetrization of neighbors that are not mutual.