Done 
.
This plays nicely with fbink_get_last_rect, and it just makes sense, so, thanks

.
(That's also a slightly sneaky way of exposing the internal fill_rect function to the API, for the more adventurous people out there who like to draw rectangle-based stuff by hand

).
Also, finally squished an annoying getopt quirk that made optional arguments w/ suboptions extremely wonky, so, proper for-real optional arguments for -s & -k

.