Explore the possibility of using libgit2

[owenthereal]

I'm starting to convert the git layer to read directly from files in the .git dir instead of shelling out to git, e.g., https://github.com/jingweno/gh/blob/pull_in_cucumber_tests/git/git.go#L87-L89. This'll improve performance by reducing the number of shell out calls.

I know libgit2 is trying to do something similar and it'd be interesting to see if we could make use of https://github.com/libgit2/git2go.

This task is not in high priority.

/cc @calavera @technoweenie

[technoweenie]

Keep in mind that this requires CGO, and would make easy cross compilation impossible.

[owenthereal]

@technoweenie Good point! But gh is already compiled against different platforms using cgo due to a limitation of cross compilation I found earlier on accessing system root certificates. I still use a cross compilation tool to build for the current platforms for i386 and amd64 though.

As a side note, I think we should set up gh build on ec2 instead of just my machine.

[technoweenie]

Ah yeah, I was aware of that issue for the mac. If we had an ec2 server, we'd still need a mac to build those binaries with CGO, right?

[owenthereal]

Yes, you're right. For now, I think we're good since I have everything set up on my computer. I created #139 to further discuss it. Travis seems to support OSX VMs but I never try it.