From the description, I'm not quite sure I understand how this API will be used. What is the `reference` parameter? Is it a blame object that I generated from an earlier call to `git_blame_file()`? Is the idea that you have an existing blame that represents the history of a file and then you call this based on some in-memory edits to overlay the blame data with new changes? Does blame ignore the working directory copy and the index copy of the file?