Separate specs from website templates

[lidel]

Extracted from https://github.com/ipfs/specs/pull/382:

:thought_balloon: would it be possible to separate content from website, so it is easier to work with for people who refuse to deal with anything other than Markdown on Github?

@darobin @hacdias how about: keep src/_includes, src/css, but everything else move to content/ or text/? I was thinking about using symlinks

[hacdias]

We don't really need symlinks as long as we change spec-generator to copy the stuff to where we need it to be I think. Or rewrite the output path by stripping the content/ from it.