Version 6.1.1 released (05-Sep-2019)

This version (Git hash value e2f9cd54...) is mainly a maintenance release, but it also serves to provide a few minor extensions:

• The Chebychev propagator has been modified such that in "relaxation" simulations (propagations in imaginary time) also excited states can be calculated. Note that this approach is usually restricted to the lowest few excited states before the method will eventually become unstable
• Added/modified a few of the examples to demonstrate the calculation of excited states by "relaxation" (propagations in imaginary time)
• Added a potential energy classdef for a chain of harmonic oscillators (model for phonons in 1D)