Generative art image evolver

File Release Notes and Changelog

Release Name: 0.2.1

Notes:
Files unpack to ./evolvotron/
See the README file for build and usage instructions.

Changes:
 - Display (not compute) priority to higher resolution images
   (saves time enlarging low res images unnecessarily)
 - Blank images on replacement (above change makes this more necessary)
 - Round-robin dispatch of done tasks to displays means redisplay more balanced.
 - -x and -X command line options to specify specifc top level function types.
 - FunctionKaleidoscope*, FunctionWindmill*, FunctionSeparateZ added.
 - More iterative functions also added: FunctionStreak Function*Ring
 - Added -f <frames> option to evolvotron_render
 - Internals: function framework changed (avoids FunctionNodeUsing::evaluate wrapper), speed improvement ?
 - Internals: Type of top-level node can mutate, MutatableImage more sane.
 - "Undo" keyboard accelerator works 
 - Per-image display "Properties" dialog added (placeholder)