Create Xcode project with framework targets.

An new Xcode project is created in order to build an iOS
framework as target. This project is Carthage compatible.

A first version of podspec is added, although pod lib lint
fails.

4 tests are failing when run through Xcode.

YogaKit/YogaKit.podspec

@@ -0,0 +1,22 @@
+Pod::Spec.new do |spec|
+  spec.name                 = 'YogaKit'
+  spec.version              = '1.0.0'
+  spec.license              = { :type => 'BSD-3-Clause', :file => '../LICENSE' }
+  spec.homepage             = 'https://facebook.github.io/yoga/'
+  spec.authors              = {
+                              'Emil Sjölander'      => 'sjolander.emil@gmail.com',
+                              'Dustin Shahidehpour' => 'dshahidehpour@gmail.com'
+                            }
+  spec.summary              = 'Yoga is a cross-platform layout engine which implements Flexbox.'
+  spec.description          = <<-DESC
+  Yoga is a cross-platform layout engine which implements Flexbox.
+  It enables maximum collaboration within your team by implementing an API familiar to
+  many designers and opening it up to developers across different platforms.
+  DESC
+  spec.documentation_url    = 'https://facebook.github.io/yoga/docs/getting-started/'
+  spec.source               = { :git => 'https://github.com/facebook/yoga.git', :tag => "v#{spec.version}" }
+  spec.platform             = :ios
+  spec.source_files         = './YogaKit/*.m', '../yoga/*.c'
+  spec.public_header_files  = './YogaKit/YogaKit.h', './YogaKit/YGLayout.h', './YogaKit/UIView+Yoga.h', '../yoga/YGEnums.h'
+  spec.private_header_files = '../yoga/*.h', './YogaKit/YGLayout+Private.h'
+end