Add scale and documentation for translation

Express translate in terms of the native matrix method instead.

libraries/Native/Transform2D.js

@@ -37,9 +37,6 @@ Elm.Native.Transform2D.make = function(elm) {
      var s = Math.sin(t);
      return new A([c, -s, 0, s, c, 0]);
  }
- function translation(x,y) {
-   return new A([1,0,x,0,1,y]);
- }
  function rotate(t,m) {
      var c = Math.cos(t);
      var s = Math.sin(t);
@@ -86,7 +83,6 @@ Elm.Native.Transform2D.make = function(elm) {
      identity:identity,
      matrix:F6(matrix),
      rotation:rotation,
-     translation:F2(translation),
      multiply:F2(multiply)
      /*
      transform:F7(transform),

libraries/Transform2D.elm

@@ -46,8 +46,26 @@ Given an angle t, it creates a counterclockwise rotation matrix:
 rotation : Float -> Transform2D
 rotation = Native.Transform2D.rotation
 
+{-| Creates a transformation matrix for translation:
+
+    translation x y
+
+          / 1 0 x \
+          | 0 1 y |
+          \ 0 0 1 /
+-}
 translation : Float -> Float -> Transform2D
-translation = Native.Transform2D.translation
+translation x y = matrix 1 0 0 1 x y
+
+{-| Creates a transformation matrix for scaling by a all directions:
+
+    scale a
+
+        / a 0 \
+        \ 0 a /
+-}
+scale : Float -> Transform2D
+scale a = matrix a 0 0 a 0 0
 
 {-| Creates a transformation for horizontal scaling -}
 scaleX : Float -> Transform2D