Hi,
About the 1:1 mapping thing is just freedom of choice I guess. I chose to separate the image (so you can use eg. different colored versions without changing the mapping - which saves memory), the number of tiles (for some reason it just sounded practical), and the character maps. The reason you can only use 8 different character maps is basically because it is much easier to program that way. I have a new version that removes this limit, but it is coming together pretty slowly, and it also allows padding + cropping (so that you can also use glowing characters and make them overlap partially).
Cheers!
Sven B