Creates a managed shader program that will poll shader files on disk
and load them automatically if their write-times change. This can be used for
easily developing shader code while the program is running. If the shader code
does not compile for any reason, errors will be displayed on the *error-output*
and a program specified by gl:*fallback-synchronizing-program* will be returned
instead (a black and yellow striped static pattern).

For an example, please see examples/synchronized-shader.lisp.