v0.4.2

A Windows fix for Rust users. Nothing else changed — if you are not building
the Rust crate on Windows, 0.4.1 is equivalent.

Still alpha: features, APIs, and the set of supported platforms are all in
flux. Verified on Linux (Ubuntu, x86-64), macOS (Apple Silicon), and Windows
(x86-64).

Fixes

• cargo build failed to link on Windows. The crate compiled its C++ core
  against the release C runtime while cargo's default (debug) profile linked
  the debug one, so the link died on unresolved external symbol __imp__calloc_dbg. --release happened to work; the default did not. (#107)

Release tooling

• CI now builds a real Rust consumer on Windows, in both debug and release. No
  job had ever run cargo on Windows, which is why the above shipped. (#107)