Undo tree

`(defhydra hydra-undo-tree (:color yellow :hint nil ) " p: undo n: redo s: save l: load " ("p" undo-tree-undo) ("n" undo-tree-redo) ("s" undo-tree-save-history) ("l" undo-tree-load-history) ("u" undo-tree-visualize "visualize" :color blue) ("q" nil "quit" :color blue))

(global-set-key (kbd "C-x u") 'hydra-undo-tree/undo-tree-undo)`

Every symmetric function pair should have its own hydra - undo/redo included.