Read/write refs on this (#125)

Fixes #123

Using the `ref` prop writes the ref to the `this.refs` object.

However, setting a ref with a callback is not allowed to write to the frozen `this.refs`. The `writeRef` props writes directly to `this` instead.

src/React.js

@@ -43,8 +43,7 @@ exports.getChildren = getChildren;
 function readRefImpl (this_) {
   return function(name) {
     return function() {
-      var refs = this_.refs || {};
-      return refs[name];
+      return this_[name];
     }
   }
 }
@@ -54,9 +53,7 @@ function writeRef(this_) {
   return function(name) {
     return function(node) {
       return function() {
-        var refs = this_.refs || {};
-        refs[name] = node;
-        this_.refs = refs;
+        this_[name] = node;
         return {};
       }
     }

src/React/DOM/Props.purs

@@ -301,13 +301,16 @@ radioGroup = unsafeMkProps "radioGroup"
 readOnly :: Boolean -> Props
 readOnly = unsafeMkProps "readOnly"
 
+-- | You can use `ref` to store a reference on `this.refs`.
+-- | To access the stored reference, `getRefs` can then be used.
 ref :: String -> Props
 ref = unsafeMkProps "ref"
 
--- | You can use `writeRef` to store a reference on `Refs`.
+-- | You can use `writeRef` to store a reference on `this`.
 -- | ```purescript
 -- | div [ withRef (writeRef this "inputElement") ] [...]
 -- | ```
+-- | To access the stored reference, `readRef` can then be used.
 withRef
   :: forall access eff
    . (Nullable Ref -> Eff (refs :: ReactRefs (write :: Write | access) | eff) Unit)