Added varargout to wave_field_mono_nfchoa_25d
Merge branch 'threed' of github.com:sfstoolbox/sfs into threed

* 'threed' of github.com:sfstoolbox/sfs:
  Added automatic plotting to wave_field_mono if now argout is given
  Added variable varargout handling to wave_field_mono_point_source etc.
  Used varargin to simplify the point_source etc. function