Renamed NSIndexPath+MPRemoveFirstIndex Category to NSIndexPath+MPReverseIndexPath

Added MPDisplayExtension Category to MPExpression and MPFunction
Added Methods to Invalidate the Cache to MPExpressionLayout and MPFunctionLayout

MathPad/MPFunctionLayout.m

@@ -73,6 +73,15 @@
 - (void)invalidate
 {
     _valid = NO;
+    [self.parent invalidate];
+}
+
+- (void)editedChildAtIndex:(NSUInteger)index
+{
+    if ([self hasCacheForChildAtIndex:index]) {
+        _childCache[index] = [NSNull null];
+    }
+    [self invalidate];
 }
 
 - (BOOL)hasCacheForChildAtIndex:(NSUInteger)index