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. Well, at least a few 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)