Use regex matching last part only, explicitly set global array to empty.

* Since I don't support directories at this point, change regex to match only if the last part of the path is in the form foo#key=value
* Explicitly set global array prehash_to_castlename to empty on each new invocation of calc_repo_var_castlename_scores() removing the requirement to unset it after use
* Add comment that inside my code, var_filename means any file or symlink matching the form foo#key=value (so not a path, just the filename; same as basename "/whatever/foo#key=value" would return)
Revert to not remove everything but filename, since files with the same name might exist inside different directories. Score is, for now, calculated based on filename only though.
Add support for track command.
Merge branch 'feature/add_track_support' into develop