Garbage collection protection
Update libgit2 binaries to e87d9d3

https://github.com/libgit2/libgit2/compare/711333e...e87d9d3
Added extension methods NoteCollection.Add and Remove that guess committer and author from config

Similar to Repository.Commit, NoteCollectionExtensions.Add/Remove take the committer and author signature from the global git config user.name / user.email. This allows modifying notes without specifying the commiter explicitly