Nikola - beware of the slug!
Nikola uses the slug of a post or page to generate the output files and directories. So if you (for any reason) decide to rename a source file, remember to rename the slug also. Or else you will spend frustrating time wondering why nikola persists in rendering something at an old location. Perhaps you will try clearing the cache, removing the doit database, or even clearing the output directory and getting even more frustrated when it doesn't help.