Add CHANGELOG.md documenting v0.1.0 and v1.0.0 changes

- Document removal of Windows ARM32 support in v1.0.0
- List all new features (version macros, release workflow, updates)
- Follow Keep a Changelog format

Author: kristjanvalur

CHANGELOG.md

@@ -0,0 +1,45 @@
+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [1.0.0] - 2025-11-16
+
+### Added
+- Version macros in `stackman.h`: `STACKMAN_VERSION_MAJOR`, `STACKMAN_VERSION_MINOR`, `STACKMAN_VERSION_PATCH`, `STACKMAN_VERSION`, `STACKMAN_VERSION_NUMBER`
+- Automated release workflow for tagged versions
+
+### Changed
+- Updated GitHub Actions to v4 (from v2)
+- README updated with complete platform list, CI information, and release documentation
+
+### Removed
+- **BREAKING**: Dropped Windows ARM32 (win_arm) support
+  - Microsoft Windows SDK 10.0.26100.0+ no longer supports 32-bit ARM development
+  - ARM32 Windows devices (Windows RT) are obsolete
+  - ARM64 Windows remains fully supported
+
+### Fixed
+- Fixed typos in documentation and source files
+- Corrected "callee-stored" → "callee-saved" terminology
+
+## [0.1] - 2020-05-18
+
+### Added
+- Core stack manipulation API: `stackman_switch()` and `stackman_call()`
+- Support for 8 platforms:
+  - Linux: sysv_amd64, sysv_i386, arm32 (AAPCS), aarch64 (AAPCS64)
+  - Windows: win_x86, win_x64, win_arm (32-bit ARM), win_arm64
+- Compiler support: GCC, Clang, MSVC (VS2017, VS2019, VS2022)
+- Pre-built libraries for all supported platforms
+- Inline assembly and separate assembly file options
+- Cross-compilation support for Linux (x86, ARM32, ARM64)
+- QEMU-based testing for ARM platforms in CI
+- Comprehensive test suite (test.c, test_cc.cc, test_static.c, test_asm.c)
+- GitHub Actions CI for automated building and testing
+- Visual Studio project files (VS2017, VS2019, VS2022)
+
+[1.0.0]: https://github.com/stackless-dev/stackman/releases/tag/v1.0.0
+[0.1]: https://github.com/stackless-dev/stackman/releases/tag/v0.1