Added first stab at a CHANGELOG

Signed-off-by: Daniel Egger <daniel@eggers-club.de>

CHANGELOG.md

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+# Change Log
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](http://keepachangelog.com/)
+and this project adheres to [Semantic Versioning](http://semver.org/).
+
+## [Unreleased]
+
+### Added
+
+- Reworked GPIOs and added fully erased pins
+- Timer support
+- Support for STM32F070
+- Additional peripheral support for STM32F030
+- Watchdog support
+
+### Changed
+
+- Removed superfluous use statements
+- Re-added Send ability for U(S)ART Rx/Tx
+
+### Fixed
+
+- Fixed some comments
+- Changed some prelude aliases to reflect crate name
+
+### Removed
+
+- Examples requiring additional driver crates
+
+## [v0.9.0] - 2018-12-17
+
+### Added
+
+- Toggleable implementation for GPIOs
+- Initial support for STM32F030
+- LICENSE file
+
+### Changed
+
+- Updated stm32f0 dependency to v0.5.0.
+- Interrupt handler to new #[interrupt] attribute
+
+[Unreleased]: https://github.com/stm32-rs/stm32f0xx-hal/compare/v0.9.0...HEAD
+[v0.9.0]: https://github.com/stm32-rs/stm32f0xx-hal/compare/v0.8.0...v0.9.0