Add a little color to linkbot - '$ green GOOD TO GO'

In Linkbot, print messages in color when in an ANSI-compatible shell.

## Usage
    $ green Hellz yeah!
    => Hellz yeah!
    $ red I don't think so.
    => I don't think so. 

## Supported colors

- black
- red
- green
- yellow
- blue
- magenta
- cyan
- white