jwir3

/**
 * Draw an arrowhead on a line on an HTML5 canvas.
 *
 * Based almost entirely off of http://stackoverflow.com/a/36805543/281460 with some modifications
 * for readability and ease of use.
 *
 * @param context The drawing context on which to put the arrowhead.
 * @param from A point, specified as an object with 'x' and 'y' properties, where the arrow starts
 *             (not the arrowhead, the arrow itself).
 * @param to   A point, specified as an object with 'x' and 'y' properties, where the arrow ends