Feature: Discard changes to work tree

[Piturnah]

Would be cool to be able to press d to discard changes to a hunk or file. I really think this should have a confirmation though, at least by default.

[Piturnah]

Note: this is essentially gonna be resetting the changes to HEAD, I believe

[Piturnah]

Ok, so it looks like Git does not support directly resetting a particular hunk. I have a proposed workaround for this, but it could be risky if it doesn't work as I expect under some edge cases.

Option 1

Under the hood, when you go to reset a hunk, gex can:

1. Stage everything other than the selected hunk
2. Commit
3. Reset hard to HEAD
4. Reset --soft to the previous commit

While typing this out I just though already of a super common case where this won't work: the case where you already have some hunks/files staged. Ugh. Leaving here just in case I think of a way to include that case

Option 2

We find some way to do this using libgit since we are already depending on it anyway.