Python module for adaptive umbrella sampling

This module can be used to perform adaptive umbrella sampling of a multi-dimensional potential of mean force. The algorithm involves::

1. calculate the free energy landscape
2. Among existing windows, select windows with E < E_max
3. For each selected window, generate 3^N-1 neighbor windows
4. Sample new windows, then go to 1) or stop if no new windows can be found

For more details about the algorithm: See

Self-Learning Adaptive Umbrella Sampling Method for the Determination of Free Energy Landscapes in Multiple Dimensions (Wojtas-Niziurski†, Meng, Roux, Bernèche, 2013) (https://doi.org/10.1021/ct300978b)