More general coordinate handling

• logCoords and basis are now arrays to allow for multiple logarithmic
  coordinates instead of only one.
• there are now additional inputs to LoadData (and thus also
  TransformCoords): reverseCoords and revCenter. These are arrays that
  tell pv_atmos which coordinates should be reversed (such as e.g.
  pressure), and around which value
• The example files as well as the test_functions file now ask for the
  path to pv_atmos instead of assuming something.
• Example and test files are modified to take into account the changes
  to pv_atmos mentioned above