rbm

This should prevent things like #701
It would be great to generate automatically the list of oldest dependencies with something like

import pkg_resources

package = pkg_resources.working_set.by_key["netket"]

oldest_dependencies = []

for requirement in package.requires():
    dependency = requirement.project_name
    if requirement.extras:
        dependency += '[' + ','.

Check and implement if possible, the use of sparse matrices instead of dense ones so that CUDA doesn't throw Out of Memory error while allocating a large tensor.