Started to Implement Evaluation

Corrected Some Errors
Cleaned Code

MathPad/MPLayout.h

@@ -41,6 +41,8 @@
 - (void)invalidate;
 
 #pragma mark Calculation and Drawing Methods
+- (CTLineRef)createLineForString:(NSString *)aString;
+
 @property (nonatomic, getter = isFlipped) BOOL flipped;
 @property (nonatomic) BOOL usesSmallSize;
 - (NSRect)bounds;