"Undo" after leaving mc mode will restore cursors as they was

If you accidentaly leave mc mode, you may return to it and restore state of cursors just by pressing C-_ .
Also this is the feature was requested in https://github.com/magnars/multiple-cursors.el/issues/86 .
How this feature implemented: every time when multiple-cursor-mode got disabled, it adds function to restore it state in buffer-undo-list, which is used by 'undo' command. 
This feature works well with regular 'undo' and with 'undo-tree-mode'. It must work with any other undo replacement.