Add an ANSI formatter for output on the console

[J5lx]

To use the ANSI formatter, the 'format' option has to be set to 'ansi'

See it in action at https://bit.ly/luminous-ansi-demo

Features:

• Based on the LaTeX formatter (well, that’s not a feature, but I think it’s worth mentioning)
• Support for XTerm 256 colors both as text color and as background color
• Support for bold, italic, underline, and strikethrough

Known issues which will be fixed when the conversion to PSR (#31) is finished:

• line numbers are not yet supported
• Nested tokens (like escape sequences inside strings) are not yet supported.

[markwatkinson]

Wow, that video is awesome! Thanks for this.

When you say nested tokens aren't yet supported, is that what I'm seeing in the video when, e.g. the line if (!preg_match('/\.css$/i', $theme)) ends up keeping the text 'css$/i' as black?

[J5lx]

Yes, that’s it. It’s because there’s no possibility to do nested styles or such using ANSI escape sequences. I’ll see how I can solve it, but now the PSR-conversion awaits!