Fix max-width and don't wrap links

Using `em` for the max-width results in it depending on the current font used (which I think is a bad thing). This increases the width back to the original level (I've used http://julialang.herokuapp.com as a reference) and reverts https://github.com/JuliaLang/julialang.github.com/commit/dd55a10133c77e6fb8e117f60783dba774b62a30.

Also fixes the download page, see https://github.com/JuliaLang/julialang.github.com/issues/63#issuecomment-66119938.