add convenience method for MBTiles bundle resources

@@ -50,6 +50,11 @@
 
 /** @name Creating Tile Sources */
 
+/** Initialize and return a newly allocated MBTiles tile source based on a given bundle resource.
+*   @param name The name of the resource file. If name is an empty string or `nil`, uses the first file encountered of the supplied type.
+*   @param extension If extension is an empty string or `nil`, the extension is assumed not to exist and the file is the first file encountered that exactly matches name. */
+- (id)initWithTileSetResource:(NSString *)name ofType:(NSString *)extension;
+
 /** Initialize and return a newly allocated MBTiles tile source based on a given local database URL.
 *   @param tileSetURL Local file path URL to an MBTiles file.
 *   @return An initialized MBTiles tile source. */

@@ -46,6 +46,11 @@
 
 @synthesize cacheable = _cacheable, opaque = _opaque;
 
+- (id)initWithTileSetResource:(NSString *)name ofType:(NSString *)extension
+{
+    return [self initWithTileSetURL:[NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:name ofType:extension]]];
+}
+
 - (id)initWithTileSetURL:(NSURL *)tileSetURL
 {
 	if ( ! (self = [super init]))