v0.0.4 — MIT relicense, docs refresh, green CI

Maintenance release: MIT relicense, refreshed docs, and a green CI again. No
changes to the public API or behaviour — Parse, the struct tags, and the
supported types are unchanged.

Added

• CONTRIBUTING.md covering setup, the test/lint workflow, code style, how to add
  a supported type, and the commit/PR/release process.
• A CHANGELOG.md (Keep a Changelog format), with history reconstructed back to
  v0.0.1.

Fixed

• CI is green again. The workflow tested Go 1.14–1.17, which have no darwin/arm64
  builds and failed to install on the now-Apple-Silicon macOS-latest runners,
  cancelling the whole matrix. It now tests the module floor (1.18) plus the two
  latest Go releases, sets fail-fast: false, and upgrades to
  actions/checkout@v4, actions/setup-go@v5, and codecov/codecov-action@v5.

Changed

• Relicensed from the Apache License 2.0 to the MIT License.
• Reworked README.md: status badges, a tag reference table, the full supported-type
  list, an explicit default-precedence rule (CLI flag > envVar > value > zero
  value), and a runnable example.

Full changelog: v0.0.3...v0.0.4