Unify boolean flag naming confention, getter spacing, and property attribute naming

Summary:
* Fixes #3
* Ordering: atomicity, then [optional] readonly, then value semantics (retain/copy/assign)
* Removed redundant `readwrite`
* No spaces between "getter = name" ("getter=name" instead)
* Property method overrides renamed as well
* self.isBlah, while technically not entirely correct, still resolves to [self blah], so left alone (@kimon had advice on this sort of naming issue last summer), and largely inconsequential

Test Plan:
* Compile and run

AsyncDisplayKit/ASImageNode.h

@@ -23,7 +23,7 @@ typedef NS_ENUM(NSUInteger, ASImageNodeTint) {
 
 #pragma mark - Cropping
 //! @abstract Indicates whether efficient cropping of the receiver is enabled. Defaults to YES. See -setCropEnabled:recropImmediately:inBounds: for more information.
-@property (nonatomic, assign) BOOL cropEnabled;
+@property (nonatomic, assign, getter=isCropEnabled) BOOL cropEnabled;
 
 /**
  @abstract Enables or disables efficient cropping.