add apply support to repository

[extrawurst]

after adding the necessary sys code (#531) this adds the new apply method to Repository and a new apply module handling the new ApplyOptions and c-callbacks.

(this is related to #403)

[alexcrichton]

Nice!

[extrawurst]

@alexcrichton can we have a point release with this? 😏

[alexcrichton]

Sure thing, done!

[mainrs]

Hey! Sorry to kind of necro this, but I have a question regarding this PR. Is this meant to be used with files produced by git diff's output? E.g. .patch files that can be applied to repositories? If so, how exactly? The documentation mentions that the Diff object is created with one of the diff_ methods on Repository, but that wouldn't apply for the above example.

Maybe I just misunderstood the purpose of this PR...

[extrawurst]

@sirwindfield I think this kind of question fits more into libgit2, git2-rs is only a wrapper around it. I am using apply to do hunk by hunk staging in gitui, maybe this helps you: https://github.com/extrawurst/gitui/blob/master/asyncgit/src/sync/hunks.rs

[mainrs]

I opened a discussion on their repository. The feature is relatively new and I am the first one, but I hope someone answers it haha. Just for reference: libgit2/libgit2#5588

@extrawurst hunk by hunk (as you did it) does still compare between the index and the current file, doesn't it?