Added Triangle.CenterOn to place a triangle on an xy coord.

v3/src/geom/triangle/CenterOn.js

@@ -0,0 +1,18 @@
+var Centroid = require('./Centroid');
+var Offset = require('./Offset');
+
+var CenterOn = function (triangle, x, y, centerFunc)
+{
+    if (centerFunc === undefined) { centerFunc = Centroid; }
+
+    //  Get the center of the triangle
+    var center = centerFunc(triangle);
+
+    //  Difference
+    var diffX = x - center.x;
+    var diffY = y - center.y;
+
+    return Offset(triangle, diffX, diffY);
+};
+
+module.exports = CenterOn;