Update Subliminal to use appledoc 2.2.

[wearhere]

At the least, this will entail that we document enum values and bitmasks (tomaz/appledoc#378).

[wearhere]

We should wait to tackle this until there's an explanation of how to document enum values and bitmasks beyond this screenshot. Appledoc's documentation is currently down…

It would also be nice to update .travis.yml to use an archived release of Appledoc 2.2 (e.g. Homebrew/homebrew-versions#204) rather than have to point to a specific (new) version of the main Appledoc formula like we're doing currently.

[wearhere]

This is worth doing for 2.0, but only so that we're "completely" documented before switching to Cocoadocs (#195)--and if this turns out to be a huge pain (considering that Appledoc's documentation still isn't back up), we should let this go.