variable parameter functions now work in multiple-parameter trials.  Introduced a new bug, though--trials no longer fully complete.
fixed trial completion bug. Found new bug.
fixed trial completion bug. Found new bug.
bug fixed. Suggest changing Trial.params into a @property to avoid future user confusion. Found new bug: timer returns True the first time it is called.  This ruins the first time a trial runs.
fixed timer bug.
added distance2D() to utils functions.