16/May/01
added
on makeRect(side) --makes a rect this on a side
on scaleRect(theRect, scaleFactor) --makes a rect this on a side
to centreRectOnPoint(theRect, thePoint) --currently inefficient two-pass version
on getCentroid(theRect)

<!--29/4/01 tim bates-->
started adding handlers to help dealing with rectangles
on getCentroid(theRect) --takes a l,t,r,b or l,t,r,b

<!--27/4/01 tim bates-->

created this new library to help with screen computations, in particular, working with eye tracking
if you tell it the physical measurements of screen width and height, and distance to the screen, then the library computes a bunch of derivative stuff such as pixels per degree.

Also included is the beginning of handler fmaily for working with rectangles

Finally a handler is included (with associated properties) which calculates the parameters required for a smooth pursuit stimulus on a linear path.