Add colors and improve alignment in the list display

[Calinou]

This adds colors to the list display and makes it easier to read by aligning alias names to the right.

Tested on:

• zsh 5.5.1 on Fedora 28,
• Bash 4.4.23 on Fedora 28,
• Bash 3.2.57 on macOS 10.13.

Preview:

Should there be a CLI argument for disabling colored output? I can add this if desired.

This closes #35.

[iridakos]

Awesome, thank you very much for the contribution!

I don't mind about the CLI argument, whatever you like :)