zrtp 0.1.0

RFC 6189 ZRTP protocol core, crypto helpers, and embeddable engine
Documentation
# Contributing

## Commits

- Use short, imperative commit subjects.
- Include a brief body only when it adds useful context.
- Sign commits with `git commit -s` so the `Signed-off-by` trailer is present.
- Keep commit messages focused on the change and the reason for it; no special Lore-style header format is required.

## Local checks

```bash
cargo fmt --all
cargo clippy --all-targets --all-features -- -D warnings
cargo test --all-features
```

## Fuzzing

```bash
cargo install cargo-fuzz
cargo fuzz run message_decode
```