GUI

$ swimview file1.txt file2.txt...
$ swimview


Basic functionality is:
  Just be able to render a swim file
  polygon + swimmers (triangles or circles)

Next functionality
  Able to render one of many swim files, and toggle between

  Fl_Output field: curr_swim_file name
  Hot-key for toggling through if multiple files
  maybe: Fl_Output for poly region
  maybe: Fl_Output for swimmer locations types


o GUI should have buttons for switching between swim files