Add support for the new GitHub README template.

I'd love the new GitHub README template to be available as the new default.
The current default could be renamed github_old.

[wikimatze]

Yeah, I'm working on it, and will release it at the end of the week.

[wikimatze]

It's done - see commit 078cb11

Thanks! I think it might need to be tweaked, though, because the font is not the same and the padding on <li> elements seems to be different as well. I think it could be cool if we wrapped the README in the same UI element that GItHub is using. Thoughts?

[wikimatze]

See commits b67eed8...eb1cec1 - in my eyes it should fit now.

[wikimatze]

Is the layout okay for now or should I ask the github people for their layout?

I think the layout is closer but not close enough. The original README template(old github theme) was almost identical, and I'd like the new template to have the same level of similarity. I don't think we need to ask GitHub for their markup, I think the layout can be easily matched (we're aiming for 95%+ similarity, not 100%). After that, we just need to apply similar CSS rules to make sure everything matches.

I see the old github theme is totally gone as well, I think we should keep it around, maybe as github-legacy.

[wikimatze]

github-legacy is a good idea - I will restore it this evening.