Support for GitHub commits

[danports]

I thought this code was already in master, but when I rebased my fork recently it disappeared. Was the code deleted from master? Or was this part of my fork that I never pushed?

-- A class for a commit
local Commit = {}
Commit.__index = Commit
Commit.new = function(repo, sha)
	local url = ('repos/%s/%s/git/commits/%s'):format(repo.user, repo.name, sha)
	local status, data = getAPI(url, repo.auth)
	if not status then
		error('Could not get github API from ' ..url)
	end
	return setmetatable({data = data}, Commit)
end

[danports]

Most likely I wrote this code a while ago and forgot about it...I'll clean it up and submit a PR.