Internal Redesign:

- Combined MPExpression and MPMutableExpression
- Abstracted children of MPExpression into MPExpressionElement protocol
- Abstracted most of MPExpressionLayout and MPFunctionLayout into common superclass MPLayout

MathPad/MPExpressionElement.h

@@ -0,0 +1,24 @@
+//
+//  MPExpressionElement.h
+//  MathPad
+//
+//  Created by Kim Wittenburg on 10.08.14.
+//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
+//
+
+@import Foundation;
+
+@protocol MPExpressionElement <NSObject, NSCoding>
+
+- (BOOL)isString;
+- (BOOL)isFunction;
+
+- (NSUInteger)length;
+
+- (double)doubleValue;
+- (float)floatValue;
+- (int)intValue;
+- (NSInteger)integerValue;
+- (long long)longLongValue;
+
+@end