v0.0.6

Added

• (embed) host-function registration API — register_fn + Ctx (§4.0 M1)

Other

• (roadmap) plan the host-function registration / embedding API (§4.0)
• add CI, crates.io, docs.rs, and MIT license badges to README

Added

• (embed) host-function registration API — Interp::register_fn /
  register_global_fn + Ctx (ROADMAP §4.0 milestone 1): register a Rust
  closure as a first-class JS function with spec-shaped name/length, build
  values, read/write properties, throw catchable errors, coerce arguments, and
  re-enter JS. Backed by a new Cell::HostFn registry cell; self-reentrancy is
  a clean TypeError.