Evil-style chunk folding

[justmytwospence]

It would be intuitive if the Vim folding keybinding worked for magit chunks. Eg:

• zr Opened all chunks
• za Toggled a chunk
• zc Closed all chunk
• zc Closed a fold
• zo Opened a chunk
• zO Opened a chunk recursively

Obviously, this would come at the cost of changing the keymap binding for stash operations, but that isn't very semantically named in the first place, so I personally don't see that as a huge deal.

[justbur]

Thanks. Try dbf5a64

I wasn't sure what the right choice for zr was. I also took the liberty of adding z[1-4] which would be nonstandard for vim but seem useful.

I'm open to suggestions for changes.