Tag definitions as "new", "updated", "deleted".

[zomglings]

In the locust summary, it should be clear to viewers which functions/classes have been added for the first time in the code base, which ones are merely updated, and which were removed.

[zomglings]

For new vs. updated, if changed_lines == total_lines, the definition is new. Otherwise, it is merely updated.

deleted entries is a little bit more complicated, as we are currently only analyzing files in the terminal_ref. The only role of the initial_ref is to generate the git diff.