Adds Javascript Support

Summary:
- As mentioned in the title, this PR adds Javascript support to Yoga. Two different builds are included in this PR thanks to [nbind](https://github.com/charto/nbind), which conveniently allow to target both Node.js' native addons and browser environments via asmjs with approximately the same codebase. That should solve #215.

- All tests successfully pass on both codepaths. You can run `yarn test:all` inside the `javascript` directory to test it.

- Because of a bug in nbind, the [following PR](https://github.com/charto/nbind/pull/57) needs to be merged and a new version released before this one can be safely merged as well.

- I had to use `double` types instead of `float` in the C++ bindings because of an Emscripten [bug](https://github.com/kripken/emscripten/issues/3592) where symbols aren't correctly exported when using floats.

- There's some tweaks to do before this PR is 100% ready to merge, but I wanted to have your opinion first. What do you think of this?

 ---

To do:

- [x] Ensure th
Closes https://github.com/facebook/yoga/pull/304

Reviewed By: mikearmstrong001

Differential Revision: D4375187

Pulled By: emilsjolander

fbshipit-source-id: 47248558a9506b7c512b5ef281cd12fe1a60cab7

javascript/sources/nbind.cc

@@ -0,0 +1,139 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+#include <yoga/Yoga.h>
+
+#include "./Node.hh"
+#include "./Layout.hh"
+#include "./Size.hh"
+#include "./global.hh"
+
+#define NBIND_DUPLICATE_POINTERS true
+
+#include <nbind/nbind.h>
+
+NBIND_GLOBAL()
+{
+    function(setExperimentalFeatureEnabled);
+    function(isExperimentalFeatureEnabled);
+    function(getInstanceCount);
+}
+
+NBIND_CLASS(Size)
+{
+    construct<>();
+    construct<double, double>();
+}
+
+NBIND_CLASS(Layout)
+{
+    construct<>();
+}
+
+NBIND_CLASS(Node)
+{
+    method(create);
+    method(destroy);
+
+    method(reset);
+
+    method(copyStyle);
+
+    method(setPositionType);
+    method(setPosition);
+
+    method(setAlignContent);
+    method(setAlignItems);
+    method(setAlignSelf);
+    method(setFlexDirection);
+    method(setFlexWrap);
+    method(setJustifyContent);
+
+    method(setMargin);
+
+    method(setOverflow);
+
+    method(setFlex);
+    method(setFlexBasis);
+    method(setFlexGrow);
+    method(setFlexShrink);
+
+    method(setWidth);
+    method(setHeight);
+
+    method(setMinWidth);
+    method(setMinHeight);
+
+    method(setMaxWidth);
+    method(setMaxHeight);
+
+    method(setAspectRatio);
+
+    method(setBorder);
+
+    method(setPadding);
+
+    method(getPositionType);
+    method(getPosition);
+
+    method(getAlignContent);
+    method(getAlignItems);
+    method(getAlignSelf);
+    method(getFlexDirection);
+    method(getFlexWrap);
+    method(getJustifyContent);
+
+    method(getMargin);
+
+    method(getFlexBasis);
+    method(getFlexGrow);
+    method(getFlexShrink);
+
+    method(getWidth);
+    method(getHeight);
+
+    method(getMinWidth);
+    method(getMinHeight);
+
+    method(getMaxWidth);
+    method(getMaxHeight);
+
+    method(getAspectRatio);
+
+    method(getBorder);
+
+    method(getPadding);
+
+    method(insertChild);
+    method(removeChild);
+
+    method(getChildCount);
+
+    method(getParent);
+    method(getChild);
+
+    method(setMeasureFunc);
+    method(unsetMeasureFunc);
+
+    method(markDirty);
+    method(isDirty);
+
+    method(calculateLayout);
+
+    method(getComputedLeft);
+    method(getComputedRight);
+
+    method(getComputedTop);
+    method(getComputedBottom);
+
+    method(getComputedWidth);
+    method(getComputedHeight);
+
+    method(getComputedLayout);
+}