[wiki] remove source code layout
[wiki] tighten up titles
[wiki] updating Xen boot instructions to mirari
[wiki] tweak index
[wiki] use mirari to boot xen vms
[wiki] update hello world to new `mirage-skeleton`
[wiki] add OPAM maintenance to index
[wiki] update article dates
[wiki] update `hello-world` to new skeleton (basic, basic_net)
Merge pull request #26 from mor1/master

update wiki