Add a directory capability parser

Directory capabilities are represented using an alternate set of tags on the existing capability types.

For example, URI:DIR2-CHK: tags a read capability for a directory stored in a CHK. URI:DIR2: tags a read-write capability for a directory stored in SDMF, etc.

We'll encounter strings like this when interpreting directory entries. It would be great to be able to parse them into some representation more useful than a string.

changed milestone to %Mobile: Browse directories

assigned to @jcalderone

Fixed by !2 (merged)

closed