ASTextNode expose exclusion paths

expose NSTextContainer's exclusionPaths property on ASTextNode to be able to exclude view areas from typesetting.

This implements #394

AsyncDisplayKitTests/ASTextNodeRendererTests.m

@@ -22,6 +22,7 @@
 @property (nonatomic, readwrite, assign) CGFloat lineSpacing;
 
 @property (nonatomic, readwrite, assign) CGSize constrainedSize;
+@property (nonatomic, readwrite) NSArray *exclusionPaths;
 
 @end
 
@@ -43,6 +44,8 @@
   _attributedString = [[NSAttributedString alloc] initWithString:@"Lorem ipsum" attributes:attributes];
   _truncationString = [[NSAttributedString alloc] initWithString:@"More"];
 
+  _exclusionPaths = nil;
+
   _constrainedSize = CGSizeMake(FLT_MAX, FLT_MAX);
 }
 
@@ -52,6 +55,7 @@
                                                       truncationString:_truncationString
                                                         truncationMode:_truncationMode
                                                       maximumLineCount:_maximumLineCount
+                                                        exclusionPaths:_exclusionPaths
                                                        constrainedSize:_constrainedSize];
 
 }
@@ -141,4 +145,18 @@
   }];
 }
 
+- (void)testExclusionPaths
+{
+  _constrainedSize = CGSizeMake(200, CGFLOAT_MAX);
+  [self setUpRenderer];
+  CGSize sizeWithoutExclusionPath = [_renderer size];
+
+  CGRect exclusionRect = CGRectMake(20, 0, 180, _lineSpacing * 2.0);
+  _exclusionPaths = @[[UIBezierPath bezierPathWithRect:exclusionRect]];
+  [self setUpRenderer];
+  CGSize sizeWithExclusionPath = [_renderer size];
+
+  XCTAssertEqualWithAccuracy(sizeWithoutExclusionPath.height + exclusionRect.size.height, sizeWithExclusionPath.height, 0.5, @"Using an exclusion path so the the text can not fit into the first two lines should increment the size of the text by the heigth of the exclusion path");
+}
+
 @end