Possibly missing op functions: reduce mean/std/variance, std, variance?

I've noticed that a few ops present in the python docs are missing for reasons I can't determine. Specifically reduce_mean, reduce_std, and reduce_variance. reduce_mean seems like it is just missing the reduce wrapper (it's present in math.mean) but I can't find methods for standard deviation or variance at all. I thought it might be related to #117 so I went looking through the api def protos, and there aren't any standard deviation or variance protos, but there aren't any reduce op protos either so I'm not sure what's up. Regardless of whether this is #117 or not, variance at least would be nice to have.

Commencez par comparer les opérations reduce_mean, reduce_std et reduce_variance documentées en Python avec l’implémentation math.mean existante et les protos de définition de l’API référencés dans l’issue. Consultez l’issue #117 pour le contexte associé ; le travail est considéré comme terminé lorsque les opérations prévues ainsi que leurs exigences concernant les protos ou les wrappers sont résolues et couvertes par la Java API.