Add favicon.sh, fix fg/bg bug. Mod zsh completion.

shell_scripts/favicon.sh
	-Add a script to generate favicons from a PNG.

zsh/prompt.zsh
	-Resolve my apparent inability to resume paused processes with
	`fg` or `bg`: both builtins were being overwritten by the
	functions `fg()` and `bg()`, defined in `prompt.zsh`. Rename
	them to `fgCol()` and `bgCol()` respectively.