Highlight nullable / nonnull / __block keywords

[JosephPecoraro]

Nullable syntax has existed since Xcode 7. I would expect the nullable, nonnull, _Nullable, _Nonnull keywords to be highlighted in some way (probably like other variable modifiers).

@interface A
- (void)method1:(nullable NSString *)string;
- (void)method2:(nonnull NSString *)string;
- (AAPLListItem * _Nullable)method3:(NSString * _Nonnull)name;
@property (copy, nullable) NSString *string;
@end

On a related note, I'd also expect the same with __block keyword which has been around much longer:

__block int x = 123;