Update to Mirage_kv 6.0.1

[palainp]

This PR is a naive implementation of Mirage_kv 5.0.0 (set_partial and rename), Mirage_kv 6.0.0 (allocate, use of Ptime.t, and list returning keys instead of strings). So far, the tests have been updated and pass. It as well works with mirage-sshfs with the #18 PR included.

I didn't dive too far into the code, I hope not, but I might have missed some optimizations. Don't hesitate if I need to fix some bits.

[reynir]

In mirage-kv.6.0.1 the result from list should now be an absolute path. I think that might still need to be changed in your PR :-)

[palainp]

It seems to work with dune test. I still have a write problem with mirage-sshfs (which uses set_partial, this is why I also added the tests for set_partial and rename) but it's probably on the unikernel side.

[palainp]

So the issue was on the unikernel side and not here. :)

[palainp]

Sorry for the (EDIT: multiple) force push I had left some mess that I had to clean up :/

And I also fixed my previous "fix" for the size of a file, now the size fix gives the same results with mirage-kv-mem and chamelon :)

[yomimono]

Thanks very much for this PR! It'll take me a little bit to review it but I very much appreciate the contribution and expect to merge it. Please do comment if you need to force-push again so I can be sure to put any patches on top of your most recent version before merging. :)

[palainp]

Thanks for your reply. As this is a naive implementation, it will require some additional work to address the inefficiency :)

I've only just started to understand the machinery under the hood, so it will be a while before I can do this.