Agate v0.1.0 — Crystal bindings for libgit2

First public release.

- Crystal bindings for libgit2 (repository, commit, tree, blob, reference,
  branch, tag, remote, index, diff, patch, blame, config, and more)
- Support for Crystal >= 1.13.0, libgit2 >= 1.7.2 (>= 1.9 recommended)
- Compile-time libgit2 version detection (1.7.x / 1.9.x)
- 631 specs, zero unreachable public methods
- Cross-platform: macOS, Alpine Linux, Ubuntu 24.04