add command fs-gamefill

[RodrigoDornelles]

It will be useful in the near future for tools like the IDE to be able to export a GBA game without having to recompile everything, just by doing a string replace.

• must pass a size, which must be the total size of the game string filled with the character 0xA,
  to reserve space in the ROM or executable.

command

./cli.sh fs-gamefill 4090 --dist ./dist/game.lua

template

--GLYSTART
return {meta={title='G',author='G',version='0.0.0'},callbacks={draw=function(s) s.draw.rect(0,8,8,8,8) end}}
--GLYEND