Add print styles

Feross, after getting a lot of use from your Linode articles, I thought I would contribute back these style changes which will make printouts a bit cleaner.

Specific changes:
* Set colors mostly to black on white background
* Remove some sections like meta, prev/next links, ads, and comments
* Add URL after links inside the article

I left the font sizes alone. They could probably be reduced a bit, but it looks pretty good with just these minimal changes.