Update Dynamic Mapping API's to match the rest of the 0.20.x style. Introduce support for predicate based dynamic matching.

* Rename RKDynamicMappingMatcher to RKObjectMappingMatcher since it is not strictly coupled to dynamic mapping and works with object mappings.
* Rework matchers into using a class cluster style to enable flexible subclassing to introduce additional matchers.

Code/ObjectMapping/RKObjectMappingMatcher.h

@@ -0,0 +1,75 @@
+//
+//  RKDynamicMappingMatcher.h
+//  RestKit
+//
+//  Created by Jeff Arena on 8/2/11.
+//  Copyright (c) 2009-2012 RestKit. All rights reserved.
+//
+
+#import <Foundation/Foundation.h>
+#import "RKObjectMapping.h"
+
+/**
+ The `RKObjectMappingMatcher` class provides an interface for encapsulating the selection of an object mapping based on runtime values. Matcher objects may be configured by key path and expected value or with a predicate object.
+
+ ## Key Path Matching
+
+ A key path matcher object is initialized with a key path, an expected value to be read from the key path, and an object mapping that is to be applied if the match evaluates to `YES`.  When evaluating the match, the matcher invokes `valueForKeyPath:` on the object being matched and compares the value returned with the `expectedValue` via the `RKObjectIsEqualToObject` function. This provides a flexible, semantic match of the property value.
+
+ ## Predicate Matching
+
+ A predicate matcher object is initialized with a predicate object and an object mapping that is to be applied if the predicate evaluates to `YES` for the object being matched.
+ */
+@interface RKObjectMappingMatcher : NSObject
+
+///-------------------------------------
+/// @name Constructing Key Path Matchers
+///-------------------------------------
+
+/**
+ Creates and returns a key path matcher object with a given key path, expected value, and an object mapping that applies in the event of a positive match.
+
+ @param keyPath The key path to obtain the comparison value from the object being matched via `valueForKeyPath:`.
+ @param expectedValue The value that is expected to be read from `keyPath` if there is a match.
+ @param objectMapping The object mapping object that applies if the comparison value is equal to the expected value.
+ @return The receiver, initialized with the given key path, expected value, and object mapping.
+ */
++ (instancetype)matcherWithKeyPath:(NSString *)keyPath expectedValue:(id)expectedValue objectMapping:(RKObjectMapping *)objectMapping;
+
+///--------------------------------------
+/// @name Constructing Predicate Matchers
+///--------------------------------------
+
+/**
+ Creates and returns a predicate matcher object with a given predicate and an object mapping that applies in the predicate evaluates positively.
+
+ @param predicate The predicate with which to evaluate the matched object.
+ @param objectMapping The object mapping object that applies if the predicate evaluates positively for the matched object.
+ @return The receiver, initialized with the given key path, expected value, and object mapping.
+ */
++ (instancetype)matcherWithPredicate:(NSPredicate *)predicate objectMapping:(RKObjectMapping *)objectMapping;
+
+///-----------------------------------
+/// @name Accessing the Object Mapping
+///-----------------------------------
+
+/**
+ The object mapping object that applies when the receiver matches a given object.
+
+ @see `matches:`
+ */
+@property (nonatomic, strong, readonly) RKObjectMapping *objectMapping;
+
+///-------------------------
+/// @name Evaluating a Match
+///-------------------------
+
+/**
+ Returns a Boolean value that indicates if the given object matches the expectations of the receiver.
+
+ @param object The object to be evaluated.
+ @return `YES` if the object matches the expectations of the receiver, else `NO`.
+ */
+- (BOOL)matches:(id)object;
+
+@end