Add new Rectangle.grid with cell size argument (#223)

orx-shapes/src/demo/kotlin/DemoRectangleGrid01.kt

@@ -0,0 +1,26 @@
+import org.openrndr.application
+import org.openrndr.color.ColorRGBa
+import org.openrndr.extra.shapes.grid
+
+fun main() {
+    application {
+        configure {
+            width = 800
+            height = 800
+        }
+        program {
+            extend {
+                drawer.fill = ColorRGBa.WHITE.opacify(0.25)
+                drawer.stroke = ColorRGBa.PINK
+
+                // Notice the negative gutter in this grid. It creates an
+                // overlap between the resulting rectangles.
+                val grid = drawer.bounds.grid(8, 4, 20.0, 20.0, -20.0, -20.0)
+                for (cell in grid.flatten()) {
+                    drawer.rectangle(cell)
+                    drawer.lineSegment(cell.position(0.0, 0.0), cell.position(1.0, 1.0))
+                }
+            }
+        }
+    }
+}