[MRG] Implement Sinkhorn in log-domain for WDA by jakubzadrozny · Pull Request #336 · PythonOT/POT

* for small values of the regularization parameter (reg) the current implementation runs into numerical issues (nans and infs)

* this can be resolved by using log-domain implementation of the sinkhorn algorithm

rflamary

@rflamary

* use the standard Sinkhorn solver by default (faster)

* use log-domain Sinkhorn if asked by the user