libzahl - big integer library

http://git.suckless.org/libzahl/tree/
The rationale for its creation can be found on the README file.
What do you think?

Suigin, you should delete wip branch now that it's merged.
Any advancements with STOKE so you can get rid of asm?

Also, slcon videos are out and there's one from maandree discussing libzahl. Actually, there were many great presentations this year. Did you like one in particular?