- Since moving `comments_hash` to `Stanza`, we've been using the wrong
kind of "comments": the comments for the _stanza_, not the comments
for the entire Cask.
- Add a test to ensure this actually works. There was previously an
infinite loop here due to the bad `comments`, visible in a `StanzaOrder`
cop test, which I speculatively added a failing test for. Turns out
that supporting nested stanza _ordering_ (vs. just grouping) is a
whole separate piece of work (there are multiple TODOs there already),
so I've backed that out and will do that separately.
- Since comment detection is only used in `Stanza`, move it there.
- The `stanzaify` method was only in `CaskBlock` since the other use of
`Stanza.new` was. Since it's only used in one other place, move it to
where it's used.
