expose cache countLimit. set default to 200. ref: jessesquires#492

Author: jessesquires

JSQMessagesViewController/Layout/JSQMessagesCollectionViewFlowLayout.h

@@ -167,6 +167,13 @@ FOUNDATION_EXPORT const CGFloat kJSQMessagesCollectionViewAvatarSizeDefault;
  */
 @property (assign, nonatomic) CGSize outgoingAvatarViewSize;
 
+/**
+ *  The maximum number of items that the layout should keep in its cache of layout information.
+ *
+ *  @discussion The default value is `200`. A limit of `0` means no limit. This is not a strict limit.
+ */
+@property (assign, nonatomic) NSUInteger cacheLimit;
+
 /**
  *  Computes and returns the size of the `messageBubbleImageView` property of a `JSQMessagesCollectionViewCell`
  *  at the specified indexPath. The returned size contains the required dimensions to display the entire message contents. 

JSQMessagesViewController/Layout/JSQMessagesCollectionViewFlowLayout.m

@@ -83,7 +83,7 @@ - (void)jsq_configureFlowLayout
 
     _messageBubbleCache = [NSCache new];
     _messageBubbleCache.name = @"JSQMessagesCollectionViewFlowLayout.messageBubbleCache";
-    _messageBubbleCache.countLimit = 100;
+    _messageBubbleCache.countLimit = 200;
 
     _messageBubbleFont = [UIFont preferredFontForTextStyle:UIFontTextStyleBody];
 
@@ -221,6 +221,11 @@ - (void)setOutgoingAvatarViewSize:(CGSize)outgoingAvatarViewSize
     [self invalidateLayoutWithContext:[JSQMessagesCollectionViewFlowLayoutInvalidationContext context]];
 }
 
+- (void)setCacheLimit:(NSUInteger)cacheLimit
+{
+    self.messageBubbleCache.countLimit = cacheLimit;
+}
+
 #pragma mark - Getters
 
 - (CGFloat)itemWidth
@@ -244,6 +249,11 @@ - (NSMutableSet *)visibleIndexPaths
     return _visibleIndexPaths;
 }
 
+- (NSUInteger)cacheLimit
+{
+    return self.messageBubbleCache.countLimit;
+}
+
 #pragma mark - Notifications
 
 - (void)jsq_didReceiveApplicationMemoryWarningNotification:(NSNotification *)notification