Find connection points on the edges of rectangles for drawing arrows & stuff.
From the top of index.js:
/**
* rectConnect(sourceCenter: {x, y}, sourceSize: {width, height},
* targetCenter: {x, y}, targetSize: {width, height})
* Imagine drawing a line between the centers of the source rectangle and the
* target rectangle. This function returns the intersections of this line
* with the boundaries of the two rectangles, in the format
* {source: {x, y}, target: {x, y}}.
*
* rectConnect(rectCenter: {x, y}, rectSize: {width, height}, point: {x, y})
* Imagine drawing a line between the center of the rectangle and the other
* point. This function returns the intersection of this line with the
* boundary of the rectangle, in the format {x, y}.
*/