AssetDir is now able to list the data root.

Previously, it was impossible to get a listing of entries right underneath
the data root.

Such a query is now possible by passing an empty string as data root.

toc.go

@@ -90,16 +90,19 @@ func writeTOCTree(w io.Writer, toc []Asset) error {
 // then AssetDir("data") would return []string{"foo.txt", "img"}
 // AssetDir("data/img") would return []string{"a.png", "b.png"}
 // AssetDir("foo.txt") and AssetDir("notexist") would return an error
+// AssetDir("") will return []string{"data"}.
 func AssetDir(name string) ([]string, error) {
+	node := _bintree
+	if len(name) != 0 {
 		cannonicalName := strings.Replace(name, "\\", "/", -1)
 		pathList := strings.Split(cannonicalName, "/")
-	node := _bintree
 		for _, p := range pathList {
 			node = node.Children[p]
 			if node == nil {
 				return nil, fmt.Errorf("Asset %%s not found", name)
 			}
 		}
+	}
 	if node.Func != nil {
 		return nil, fmt.Errorf("Asset %%s not found", name)
 	}