Fix yet more 3s into 3.5s

They're everywhere!
Add reference page on catalog compilation

I put it as a sibling to the one about agent/master HTTPS communications. This
came up because I needed to reference it from the site manifest page, and it
didn't exist yet.
Add page about the site manifest

As promised, we get to keep this short and sweet and just link to the
compilation page.
Improve links to main / site manifest page; rename language summary to language basics

As for the latter: I think that's more descriptive, and will make people more
likely to click on that page.
Note that import is deprecated, link to alternative
Merge branch 'puppet35'