feat: Turtle.js.step ( Fixes PoshWeb#308 )

Author: James Brundage

Types/Turtle.js/step.js

@@ -0,0 +1,7 @@
+function step(dx,dy) {
+    if (this.isPenDown) { this.steps.push(` l ${dx} ${dy} `) }
+    else { this.steps.push(` m ${dx} ${dy} `) }
+    this.x += dx; this.y += dy ; this.resize()
+    return this
+}
+