Refactor Homebrew's `Tty` class

which was incorporated into our codebase

* separate attributes from colors
* don't reset all attributes when setting a color
* allow chaining for multiple attributes
* cover all basic colors and attributes
* use more standard names *ie* `Tty#underline` instead of `Tty#em`
* add `Tty#bg_red`, *etc.*
* sanity checks
* style

This fixes some minor bugs such as the display of underline under single dash in audit output.