A Pull method was added to repository.go and git_repository.go.

This method is intended to behave like git-pull meaning it starts with

a git-fetch and then a git-merge. Fetching is made rather

straightforward thanks to git2go. However, the merge section of Pull

required a few more steps. First, a merge analysis is performed, then the

merge and lastly a commit is created.

I setup a remote repository on github, cloned it on my machine, pushed

a few changes and pulled those changes into my local copy using only

RB-Gateway's Pull method.