feat: Turtle.PenUp/PenDown() ( Fixes #46 )

Author: James Brundage

Types/Turtle/Alias.psd1

@@ -0,0 +1,7 @@
+@{
+    pd = 'PenDown'
+    pu = 'PenUp'
+    fd = 'Forward'
+    down = 'PenDown'
+    up = 'PenUp'
+}

Types/Turtle/PenDown.ps1

@@ -0,0 +1,2 @@
+$this.IsDown = $true
+return $this

Types/Turtle/PenUp.ps1

@@ -0,0 +1,2 @@
+$this.IsDown = $false
+return $this