Add API docs generated via AI Anthropic Claude Sonnet 4.5

[nbyoung-spire]

I applied the prompts copied below to Anthropic Claude with model Sonnet 4.5 in generating the content of this change, which I manually integrated with the existing README.md. Please review the result for general correctness.

Refer to the directories spacepacket and CCSDS in the multi-step documentation and programming task that follows. Focus especially on the CCSDS/ccsds_space_packet.txt document that contains sections 1 through 4 of the normative specification for the protocol that the spacepacket library implements in Rust. In the task's first step, document the Application Programming Interface (API) that the spacepacket library implements. For each CCSDS Service, Function or Feature, highlight and summarize the API's Rust public functions, types, and traits. Clearly identify each unimplemented Service, Function or Feature with an expression like "Not implemented". Also for each Service, Function or Feature, cite the relevant CCSDS standard with the document section number. Compose the document in Markdown in a file named claude_output/spacepacket-rs.md. Complete this first step before awaiting further steps that will build on these interim results.

Use only sections 1, 2, 3, and 4 from the CCSDS document. Ignore Section 5 and the Annexes.

[mkolopanis]

I like the addition of the comparisons with spec and implementation details.
I wonder if the API docs in the readme are necessary though, this crate is built on crates.io too, we could do better linking to the official docs.rs page