Handle initial commit

[dtaniwaki]

If a user creates a repository in local and make commits and modifications, then use git-ghost to run his code in remote, git-ghost cannot find the base commit because he hasn't pushed it to a remotely available location.
It's very useful if git-ghost can handle such a case.

[dtaniwaki]

You can get the content of first commit by git show --pretty=format:%b --binary $(git rev-list --max-parents=0 HEAD). We may need enhance the patch method to save and load first commits in ghost repos. Maybe, we can save it with the name of first-commit and the following commits as commits.patch, then load the first commit and patch with the commits.