Introduce a plugin changelog file.

The changelog adheres to the [Keep a Changelog](http://keepachangelog.com/en/1.0.0/) standard, and codifies our usage of semantic versioning moving forward.

Author: stevegrunwell

CHANGELOG.md

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+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
+and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
+
+## [Version 1.0.0 (Beta 2)] - 2017-12-22
+
+* Clean up codebase to adhere to the [WordPress coding standards](https://make.wordpress.org/core/handbook/best-practices/coding-standards/), and introduce an `.editorconfig` to make this kind of change less likely in the future ([#8])
+* Introduced automated unit tests via the WordPress core test suite ([#9])
+* Fixed bug where custom database table was not being created upon plugin activation ([#5], [#9])
+* General documentation updates ([#2])
+
+## [Version 1.0.0 (Beta 1)] - 2017-10-02
+
+* Initial public release of the plugin in a beta state.
+
+
+[Unreleased]: https://github.com/liquidweb/woocommerce-order-tables/compare/master...develop
+[Version 1.0.0 (Beta 2)]: https://github.com/liquidweb/woocommerce-order-tables/releases/tag/v1.0.0-beta.2
+[Version 1.0.0 (Beta 1)]: https://github.com/liquidweb/woocommerce-order-tables/releases/tag/v1.0.0-beta.1
+[#2]: https://github.com/liquidweb/woocommerce-order-tables/pull/2
+[#5]: https://github.com/liquidweb/woocommerce-order-tables/pull/5
+[#8]: https://github.com/liquidweb/woocommerce-order-tables/pull/8
+[#9]: https://github.com/liquidweb/woocommerce-order-tables/pull/9