Links are hard to differentiate on cython.org

[gwerbin]

Copied from cython/cython#2677 (comment)

It's very hard to tell links apart from regular text on the Cython homepage. Example screenshot on Imgur.

This is undesirable from a general UX perspective and can be an issue for accessibility. Is there any reason they can't be a slightly brighter shade, and/or underlined?

They also don't change on-hover or if they've already been followed. Is there any reason not to set this?

[gwerbin]

Now that I'm looking over the site again, I feel like it could do with some re-organization by:

• putting the "Useful Links" section next to the "Documentation" section
• tightening up the body copy to make it easier to read (I don't think the bold text chunks are helping)

Since that's a bigger change, I won't do it in the same PR. Don't want to step on any toes here, either-- just a huge fan of Cython, trying to make sure it's easy for others to find information on.