Node placeholder API

ASDisplayNodes now have an overidable method -placeholderImage that lets you provide a custom UIImage to display while a node is displaying asyncronously. The default implementation of this method returns nil and thus does nothing. A provided example project also demonstrates using the placeholder API.

AsyncDisplayKit/ASTextNode.h

@@ -69,6 +69,18 @@ typedef NS_ENUM(NSUInteger, ASTextNodeHighlightStyle) {
  */
 @property (nonatomic, readonly, assign) NSUInteger lineCount;
 
+#pragma mark - Placeholders
+
+/**
+ @abstract The placeholder color.
+ */
+@property (nonatomic, strong) UIColor *placeholderColor;
+
+/**
+ @abstract Inset each line of the placeholder.
+ */
+@property (nonatomic, assign) UIEdgeInsets placeholderInsets;
+
 #pragma mark - Shadow
 
 /**