Support anchor links

[idleberg]

Many README files use anchors to link particular sections within the file. This works great when surfing on GitHub, but not on the Atom website. Would be a nice-to-have feature!

[piascikj]

Was just inspecting my readme and found I needed this as well.

[piascikj]

I'd be glad to implement it if granted read access to the repo.

[cori]

This actually looks like a duplicate of #42 (ha!).