Visual mode support for undotree

It would be great to be able to select a chunk of text (via the VISUAL modes) and for undotree to only undo changes in that selected part of the file.

For example this would probably work well with functions/classes/etc to only undo changes that were made to that specific structure.

This would be kind of like a poor-mans git where you don't want the overhead of committing small chunks of text when you just experiment.

[mbbill]

that's a great idea, but seems a bit difficult to implement with how the undo system works in vim