Roadmap to release 1

[indrora]

I figure now is as good a time as ever to outline the things that need to happen for release 1 of the spec, most of which are related to the reference archiver.

non-archiver deficiencies:

• docs: need to finalize some wording
• docs/theme: finish GOAT diagram work
• docs/theme: finish upstream pull request Begin fixing landing customization colinwilson/lotusdocs#148
• format: SDDL strings??? (Windows SDDL strings vs. binary representation choice #4)

archiver deficiencies:

• parc/cmd/create: add os-specific metadata #8
• parc/cmd/extract: implement #7
• parc/cmd/verify: cleaner implement

ponzu/lib deficiencies:

• ponzu: OS-specific metadata extraction & re-application #6

[indrora]

Additional spots:

• Additional compressor options? I want to add S2 (used by MinIO) but there's only one reference compressor from @klauspost; I'm hesitant to add something that doesn't have a good description outside of a single reference implementation.
• A "tape safe" version that indexes on 512byte blocks as an "extension"?