wording tweaks to overview
Merge branch 'master' of https://github.com/mirage/mirage-www

Conflicts:
	tmpl/wiki/overview-of-mirage.md
[wiki] update dates on install and hello-world posts
revert bad overview tweaks
merge amir's latest commit to overview
update links to opam.ocaml.org in install
typo
helloworld tweaks
remove broken wiki posts from index for now
Merge branch 'master' of https://github.com/mirage/mirage-www