another MBTiles convenience method

@@ -50,6 +50,9 @@
 
 /** @name Creating Tile Sources */
 
+/** Initialize and return a newly allocated MBTiles tile source based on a given bundle resource with the extension `.mbtiles`. */
+- (id)initWithTileSetResource:(NSString *)name;
+
 /** 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. */

@@ -46,6 +46,11 @@
 
 @synthesize cacheable = _cacheable, opaque = _opaque;
 
+- (id)initWithTileSetResource:(NSString *)name
+{
+    return [self initWithTileSetResource:name ofType:([[[name pathExtension] lowercaseString] isEqualToString:@"mbtiles"] ? @"" : @"mbtiles")];
+}
+
 - (id)initWithTileSetResource:(NSString *)name ofType:(NSString *)extension
 {
     return [self initWithTileSetURL:[NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:name ofType:extension]]];