Implement redirects on gh-pages site

[thekaveman]

We have a few redirects currently active on the Netlify site. We need to support these in the new gh-pages site as well.

[thekaveman]

This blog post has a fairly good run-down of the options, TLDR;

1. Use the (GitHub approved) JekyllRedirectFrom plugin
2. Create a Layout that does client-side redirect via <meta> tag and javascript fallback.

Personally I've used Option 2 before and it's relatively straightforward. Option 1 seems pretty easy too, but adds another Plugin that we have to deal with/learn/etc. I'm going to submit a PR for Option 2 and let the team review/approve/reject.