ShengBTE v1.4.0 released

Version v1.4.0 of ShengBTE has been released and can be obtained from the Downloads section. This version is focused on a major overhaul of the parallelization scheme, contributed by Ben Durham. ShengBTE is now a hybrid OpenMP+MPI application. Using threads instead or in addition to processed can lead to better performance and significantly reduced memory usage. See README.md for some details.