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/Node.hh

@@ -0,0 +1,174 @@
+/**
+ * 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.
+ */
+
+#pragma once
+
+#include <memory>
+
+#include <nbind/api.h>
+#include <nbind/BindDefiner.h>
+#include <yoga/Yoga.h>
+
+#include "./Layout.hh"
+#include "./Size.hh"
+
+class Node {
+
+ public:
+
+    static Node * create(void);
+    static void destroy(Node * node);
+
+ public:
+
+    static Node * fromYGNode(YGNodeRef nodeRef);
+
+ private:
+
+    Node(void);
+
+ public:
+
+    ~Node(void);
+
+ public: // Prevent accidental copy
+
+    Node(Node const &) = delete;
+
+    Node const & operator=(Node const &) = delete;
+
+ public:
+
+    void reset(void);
+
+ public: // Style setters
+
+    void copyStyle(Node const & other);
+
+    void setPositionType(int positionType);
+    void setPosition(int edge, double position);
+
+    void setAlignContent(int alignContent);
+    void setAlignItems(int alignItems);
+    void setAlignSelf(int alignSelf);
+    void setFlexDirection(int flexDirection);
+    void setFlexWrap(int flexWrap);
+    void setJustifyContent(int justifyContent);
+
+    void setMargin(int edge, double margin);
+
+    void setOverflow(int overflow);
+
+    void setFlex(double flex);
+    void setFlexBasis(double flexBasis);
+    void setFlexGrow(double flexGrow);
+    void setFlexShrink(double flexShrink);
+
+    void setWidth(double width);
+    void setHeight(double height);
+
+    void setMinWidth(double minWidth);
+    void setMinHeight(double minHeight);
+
+    void setMaxWidth(double maxWidth);
+    void setMaxHeight(double maxHeight);
+
+    void setAspectRatio(double aspectRatio);
+
+    void setBorder(int edge, double border);
+
+    void setPadding(int edge, double padding);
+
+ public: // Style getters
+
+    int getPositionType(void) const;
+    double getPosition(int edge) const;
+
+    int getAlignContent(void) const;
+    int getAlignItems(void) const;
+    int getAlignSelf(void) const;
+    int getFlexDirection(void) const;
+    int getFlexWrap(void) const;
+    int getJustifyContent(void) const;
+
+    double getMargin(int edge) const;
+
+    int getOverflow(void) const;
+
+    double getFlexBasis(void) const;
+    double getFlexGrow(void) const;
+    double getFlexShrink(void) const;
+
+    double getWidth(void) const;
+    double getHeight(void) const;
+
+    double getMinWidth(void) const;
+    double getMinHeight(void) const;
+
+    double getMaxWidth(void) const;
+    double getMaxHeight(void) const;
+
+    double getAspectRatio(void) const;
+
+    double getBorder(int edge) const;
+
+    double getPadding(int edge) const;
+
+ public: // Tree hierarchy mutators
+
+    void insertChild(Node * child, unsigned index);
+    void removeChild(Node * child);
+
+ public: // Tree hierarchy inspectors
+
+    unsigned getChildCount(void) const;
+
+    // The following functions cannot be const because they could discard const qualifiers (ex: constNode->getChild(0)->getParent() wouldn't be const)
+
+    Node * getParent(void);
+    Node * getChild(unsigned index);
+
+ public: // Measure func mutators
+
+    void setMeasureFunc(nbind::cbFunction & measureFunc);
+    void unsetMeasureFunc(void);
+
+ public: // Measure func inspectors
+
+    Size callMeasureFunc(double width, int widthMode, double height, int heightMode) const;
+
+ public: // Dirtiness accessors
+
+    void markDirty(void);
+    bool isDirty(void) const;
+
+ public: // Layout mutators
+
+    void calculateLayout(double width, double height, int direction);
+
+ public: // Layout inspectors
+
+    double getComputedLeft(void) const;
+    double getComputedRight(void) const;
+
+    double getComputedTop(void) const;
+    double getComputedBottom(void) const;
+
+    double getComputedWidth(void) const;
+    double getComputedHeight(void) const;
+
+    Layout getComputedLayout(void) const;
+
+ private:
+
+    YGNodeRef m_node;
+
+    std::unique_ptr<nbind::cbFunction> m_measureFunc;
+
+};