* ztree/ztree-diff-model.el (ztree-diff-node): Use cl-defstruct

* ztree/ztree-diff-model.el (ztree-diff-node): Use cl-defstruct

(ztree-diff-model-partial-rescan, ztree-diff-model-subtree)
(ztree-diff-node-update-diff-from-children, )
(ztree-diff-node-traverse):
* ztree/ztree-diff.el (ztree-diff-copy-file, ztree-diff-copy-dir)
(ztree-diff-delete-file): Adjust accordingly.
* ztree/ztree-dir.el (ztree-dir): Don't quote lambda.
* ztree/ztree.el: Fix up maintainer address.  Add cl-lib dependency.
* ztree/ztree-util.el (ztree-defrecord): Delete.