Add @diml's post on utop

This is a great draft and with a few tweaks will make a great
guest post.
Fix some minor orthographic irregularities.
tweaks and edits throughout
Merge branch 'master' into utop
My edits to utop post
Update publication date of utop post
Merge pull request #15 from ocaml/utop

Add @diml's post on utop (for 26 Aug)