Fix naming convetion:

- "Layout node" is changed to "layout spec".
- Update tests.
- Update Kittens sample.

AsyncDisplayKit/Layout/ASStackLayoutSpec.h

@@ -0,0 +1,87 @@
+/*
+ *  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 <AsyncDisplayKit/ASLayoutSpec.h>
+
+typedef NS_ENUM(NSUInteger, ASStackLayoutDirection) {
+  ASStackLayoutDirectionVertical,
+  ASStackLayoutDirectionHorizontal,
+};
+
+/** If no children are flexible, how should this spec justify its children in the available space? */
+typedef NS_ENUM(NSUInteger, ASStackLayoutJustifyContent) {
+  /**
+   On overflow, children overflow out of this spec's bounds on the right/bottom side.
+   On underflow, children are left/top-aligned within this spec's bounds.
+   */
+  ASStackLayoutJustifyContentStart,
+  /**
+   On overflow, children are centered and overflow on both sides.
+   On underflow, children are centered within this spec's bounds in the stacking direction.
+   */
+  ASStackLayoutJustifyContentCenter,
+  /**
+   On overflow, children overflow out of this spec's bounds on the left/top side.
+   On underflow, children are right/bottom-aligned within this spec's bounds.
+   */
+  ASStackLayoutJustifyContentEnd,
+};
+
+typedef NS_ENUM(NSUInteger, ASStackLayoutAlignItems) {
+  /** Align children to start of cross axis */
+  ASStackLayoutAlignItemsStart,
+  /** Align children with end of cross axis */
+  ASStackLayoutAlignItemsEnd,
+  /** Center children on cross axis */
+  ASStackLayoutAlignItemsCenter,
+  /** Expand children to fill cross axis */
+  ASStackLayoutAlignItemsStretch,
+};
+
+typedef struct {
+  /** Specifies the direction children are stacked in. */
+  ASStackLayoutDirection direction;
+  /** The amount of space between each child. */
+  CGFloat spacing;
+  /** How children are aligned if there are no flexible children. */
+  ASStackLayoutJustifyContent justifyContent;
+  /** Orientation of children along cross axis */
+  ASStackLayoutAlignItems alignItems;
+} ASStackLayoutSpecStyle;
+
+/**
+ A simple layout spec that stacks a list of children vertically or horizontally.
+
+ - All children are initially laid out with the an infinite available size in the stacking direction.
+ - In the other direction, this spec's constraint is passed.
+ - The children's sizes are summed in the stacking direction.
+   - If this sum is less than this spec's minimum size in stacking direction, children with flexGrow are flexed.
+   - If it is greater than this spec's maximum size in the stacking direction, children with flexShrink are flexed.
+   - If, even after flexing, the sum is still greater than this spec's maximum size in the stacking direction,
+     justifyContent determines how children are laid out.
+
+ For example:
+ - Suppose stacking direction is Vertical, min-width=100, max-width=300, min-height=200, max-height=500.
+ - All children are laid out with min-width=100, max-width=300, min-height=0, max-height=INFINITY.
+ - If the sum of the childrens' heights is less than 200, children with flexGrow are flexed larger.
+ - If the sum of the childrens' heights is greater than 500, children with flexShrink are flexed smaller.
+   Each child is shrunk by `((sum of heights) - 500)/(number of flexShrink-able children)`.
+ - If the sum of the childrens' heights is greater than 500 even after flexShrink-able children are flexed,
+   justifyContent determines how children are laid out.
+ */
+@interface ASStackLayoutSpec : ASLayoutSpec
+
+/**
+ @param style Specifies how children are laid out.
+ @param children ASLayoutable children to be positioned.
+ */
++ (instancetype)newWithStyle:(ASStackLayoutSpecStyle)style children:(NSArray *)children;
+
+@end