Speed Boost minor compatibility fixes

Small compatibility fixes between Python 2 and 3.

Speed-boost

The lhsmdu library is now much faster (e.g.15-20 times faster for 500 samples). The code has been refactored and optimized for speed. No backward-compatibility problems expected, and no other functionality has been added in this release.

First release for this code

This is a package for generating latin hypercube samples with multi-dimensional uniformity. This allows you to also sample from arbitrary CDFs.

To cite, please cite both the original paper: http://dx.doi.org/10.1016%2Fj.jspi.2011.09.016.
and the repository: https://doi.org/10.5281/zenodo.2578781