Support for sha256 object identifiers?

[elavoie]

First, thank you for all the hard work you put in the bindings.

Second, now that the latest revisions of git, and as far as I can tell libgit2 as well, both support using sha256 for object identifiers, I am wondering how much work it would be to add this to pygit2? Is the hashing function well-encapsulated in a few places or is it a widespread assumption that sha1 is used?

If support for it did not require too much mastery over the internals of pygit2, I would be willing to take a look at it.

Cheers,

Erick