Add a macro for interleaving arbitrary processing with threading

Works by creating a wrapped function that does the processing
function (threading the argument of course) and returns the argument
passed in.  So we assume side-effects are intended.
Break up the main processing block into functions

Also use the ->interleave macro do to draw-and-sleep.  Thus creating a
slideshow of all the different steps.
Correct the threading macro to have it not expand the let name
Make the frame always on top and larger
Put back in code to remove the header
Pause for longer on each image