true_angular is not a distance?

[jlmelville]

This may be based on my lack of understanding as covered in #231 but it seems like the true_angular function returns a similarity and not a distance, i.e.:

from sklearn.datasets import load_iris

iris = np.float32(load_iris().data)

import pynndescent.distances as dist

dist.cosine(iris[0], iris[0]), dist.cosine(iris[0], iris[1])
(0.0, 0.0014208250387670596)

dist.true_angular(iris[0], iris[0]), dist.true_angular(iris[0], iris[1])
(1.0, 0.9830298038991578)

Edited to add that alternative_cosine is a distance, which is what is actually used for finding nearest neighbors when metric = "true_angular", although it gets transformed back into a similarity via true_angular_from_alt_cosine at the end).