Wavepacket 0.3.4 released

New features in this version:

• There is now a much simpler approach to build Wavepacket with a
  virtual machine.

  Install two programs (Vagrant + Virtualbox), modify a config file,
  open a console, type three to four commands, and you can execute
  Wavepacket Python code in your Web browser. For more details, see
  README_VirtualMachine in the root directory. Needs some more
  polishing, but should be reasonably plug&play.

• Plotting in Python was improved considerably.

  Plots are still limited to one dimension right now, but you can set
  the units to use for coordinates, energies etc., and it is possible
  to save the plots as animations.

• Added exponentiation of operators.

  This feature is still in its infancy, but at least basic
  functionality for certain operators is there. This will allow
  absorbing boundaries for the efficient Chebychev propagators or the
  split operator method.

I also removed some temporaries to speed up the Chebychev
propagators, and did some cleanup that will help with a Windows
release.