Made the script executable, since otherwise it won't build.
A bunch of micro-edits to try to shrink the resulting binary.

- Make all local functions static.
- Make all loops use uint8_t for the index if possible.
- Make variables and data const when possible.

Seems to gain ~3% on the final ELF, not a lot but also not intrusive at all.
Merge pull request #1 from unwind/master

Minor fixes to minimatrix