Long filename support

[inferiorhumanorgans]

As I mentioned in #9 I've been working on hacking up support for Rock Ridge extensions. The Joliet (UCS-2/UTF-16) stuff is done and relatively simple. Rock Ridge is a fair bit more complex and compounding that I used that as an excuse to pull in some collateral improvements (documentation, testing, linting, fixing the examples). Going forward I'll be maintaining this fork as cdfs, but the changes I've linked to below should involve minimal changes to the public API.

Here's the diff for the whole RR changeset against 2e29b91.

https://git.sr.ht/~az1/iso9660-rs/commit/6d48c75b59e109005472750337bf7cd73daf4313.patch