title: Get last user that modify an object
body: <p>Thank to the libgit api, I can get the Object corresponding to my entry in the tree.
  - Get the last commit (git_reference_peel)
  - Get the tree (git_commit_tree)
  - Get the tree entry (git_tree_entry_bypath)
  - Get the object (git_tree_entry_to_object)</p>
  
  <p>I wonder if there is a way to get the author/signature of the last user who has make a change on this object.</p>
  
  <p>The signature of the commit doesn't my requirement</p>
  
  <p>Best Regards
  Vincent</p>