fix ls colors on mac; update prompt; cleanup and optimize
fix ls colors on mac; update prompt; cleanup and optimize

- prefer GNU ls over BSD ls
- check for existence of fd before using it
- prompt symbol changed to ">"
- prompt is red when exit code is non-zero, else green
- prompt symbols should now be safer with other fonts

joech4n/zsh-dotfiles,joech4n/zsh-dotfiles