CocoaPods support.

Summary:
This supersedes #309 and #305.

This is still a **work-in-progress.**

**TODO**

 - [x] Create Xcode project that builds an iOS framework
 - [x] Fix failing tests on Xcode
 - [ ] Make `pod lib lint` pass and make sure YogaKit can be included using CocoaPods
 - [ ] Add `pod lib lint` to .travis.yml
 - [x] Migrate to travis osx image with Xcode 8.2

**FOLLOW-UP**
  - [ ] Make YogaKitSample use framework built by new Xcode project.
  - [ ] Make Travis to upload prebuilt versions of the framework. More [here](https://github.com/Carthage/Carthage#use-travis-ci-to-upload-your-tagged-prebuild-frameworks)
  - [ ] Upgrade github/jekyll docs about installation using Cocoapods/Carthage
Closes https://github.com/facebook/yoga/pull/352

Reviewed By: emilsjolander

Differential Revision: D4471950

Pulled By: dshahidehpour

fbshipit-source-id: 8f30c69f9a487b26aa2e5f3b66841334b01b0ab1

YogaKit/Source/YGLayout.h

@@ -0,0 +1,114 @@
+/**
+ * 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.
+ */
+
+#import <UIKit/UIKit.h>
+#import <yoga/YGEnums.h>
+
+@interface YGLayout : NSObject
+
+/**
+  The property that decides if we should include this view when calculating layout. Defaults to YES.
+ */
+@property (nonatomic, readwrite, assign, setter=setIncludedInLayout:) BOOL isIncludedInLayout;
+
+/**
+ The property that decides during layout/sizing whether or not styling properties should be applied. Defaults to NO.
+ */
+@property (nonatomic, readwrite, assign, setter=setEnabled:) BOOL isEnabled;
+
+@property (nonatomic, readwrite, assign) YGDirection direction;
+@property (nonatomic, readwrite, assign) YGFlexDirection flexDirection;
+@property (nonatomic, readwrite, assign) YGJustify justifyContent;
+@property (nonatomic, readwrite, assign) YGAlign alignContent;
+@property (nonatomic, readwrite, assign) YGAlign alignItems;
+@property (nonatomic, readwrite, assign) YGAlign alignSelf;
+@property (nonatomic, readwrite, assign) YGPositionType position;
+@property (nonatomic, readwrite, assign) YGWrap flexWrap;
+@property (nonatomic, readwrite, assign) YGOverflow overflow;
+
+@property (nonatomic, readwrite, assign) CGFloat flexGrow;
+@property (nonatomic, readwrite, assign) CGFloat flexShrink;
+@property (nonatomic, readwrite, assign) CGFloat flexBasis;
+
+@property (nonatomic, readwrite, assign) CGFloat left;
+@property (nonatomic, readwrite, assign) CGFloat top;
+@property (nonatomic, readwrite, assign) CGFloat right;
+@property (nonatomic, readwrite, assign) CGFloat bottom;
+@property (nonatomic, readwrite, assign) CGFloat start;
+@property (nonatomic, readwrite, assign) CGFloat end;
+
+@property (nonatomic, readwrite, assign) CGFloat marginLeft;
+@property (nonatomic, readwrite, assign) CGFloat marginTop;
+@property (nonatomic, readwrite, assign) CGFloat marginRight;
+@property (nonatomic, readwrite, assign) CGFloat marginBottom;
+@property (nonatomic, readwrite, assign) CGFloat marginStart;
+@property (nonatomic, readwrite, assign) CGFloat marginEnd;
+@property (nonatomic, readwrite, assign) CGFloat marginHorizontal;
+@property (nonatomic, readwrite, assign) CGFloat marginVertical;
+@property (nonatomic, readwrite, assign) CGFloat margin;
+
+@property (nonatomic, readwrite, assign) CGFloat paddingLeft;
+@property (nonatomic, readwrite, assign) CGFloat paddingTop;
+@property (nonatomic, readwrite, assign) CGFloat paddingRight;
+@property (nonatomic, readwrite, assign) CGFloat paddingBottom;
+@property (nonatomic, readwrite, assign) CGFloat paddingStart;
+@property (nonatomic, readwrite, assign) CGFloat paddingEnd;
+@property (nonatomic, readwrite, assign) CGFloat paddingHorizontal;
+@property (nonatomic, readwrite, assign) CGFloat paddingVertical;
+@property (nonatomic, readwrite, assign) CGFloat padding;
+
+@property (nonatomic, readwrite, assign) CGFloat borderLeftWidth;
+@property (nonatomic, readwrite, assign) CGFloat borderTopWidth;
+@property (nonatomic, readwrite, assign) CGFloat borderRightWidth;
+@property (nonatomic, readwrite, assign) CGFloat borderBottomWidth;
+@property (nonatomic, readwrite, assign) CGFloat borderStartWidth;
+@property (nonatomic, readwrite, assign) CGFloat borderEndWidth;
+@property (nonatomic, readwrite, assign) CGFloat borderWidth;
+
+@property (nonatomic, readwrite, assign) CGFloat width;
+@property (nonatomic, readwrite, assign) CGFloat height;
+@property (nonatomic, readwrite, assign) CGFloat minWidth;
+@property (nonatomic, readwrite, assign) CGFloat minHeight;
+@property (nonatomic, readwrite, assign) CGFloat maxWidth;
+@property (nonatomic, readwrite, assign) CGFloat maxHeight;
+
+// Yoga specific properties, not compatible with flexbox specification
+@property (nonatomic, readwrite, assign) CGFloat aspectRatio;
+
+/**
+ Get the resolved direction of this node. This won't be YGDirectionInherit
+ */
+ @property (nonatomic, readonly, assign) YGDirection resolvedDirection;
+
+/**
+ Perform a layout calculation and update the frames of the views in the hierarchy with the results
+ */
+- (void)applyLayout NS_SWIFT_NAME(applyLayout());
+
+/**
+ Returns the size of the view if no constraints were given. This could equivalent to calling [self sizeThatFits:CGSizeMake(CGFLOAT_MAX, CGFLOAT_MAX)];
+ */
+ @property (nonatomic, readonly, assign) CGSize intrinsicSize;
+
+/**
+ Returns the number of children that are using Flexbox.
+ */
+ @property (nonatomic, readonly, assign) NSUInteger numberOfChildren;
+
+/**
+ Return a BOOL indiciating whether or not we this node contains any subviews that are included in Yoga's layout.
+ */
+ @property (nonatomic, readonly, assign) BOOL isLeaf;
+
+/**
+ Mark that a view's layout needs to be recalculated. Only works for leaf views.
+ */
+- (void)markDirty;
+
+@end