Cleanup cache properly

There seems to be no way to cleanup the entire cache efficiently. Modify the removeData function to optionally do so. 

Ref: julianshapiro#644 (comment)

velocity.js

@@ -174,9 +174,15 @@
             store = id && cache[id];
 
         if (store) {
-            $.each(keys, function(_, key) {
-                delete store[key];
-            });
+           // Cleanup the entire store if no keys are provided.
+            if (!keys) {
+                delete cache[id];
+            }
+            else {
+                $.each(keys, function (_, key) {
+                    delete store[key];
+                });
+            }
         }
     };
 
@@ -3883,4 +3889,4 @@ return function (global, window, document, undefined) {
 
 /* The CSS spec mandates that the translateX/Y/Z transforms are %-relative to the element itself -- not its parent.
 Velocity, however, doesn't make this distinction. Thus, converting to or from the % unit with these subproperties
-will produce an inaccurate conversion value. The same issue exists with the cx/cy attributes of SVG circles and ellipses. */
+will produce an inaccurate conversion value. The same issue exists with the cx/cy attributes of SVG circles and ellipses. */