Add links to CHANGELOG and fix date for v0.1.18

The CHANGELOG now conforms to keepachangelog.com. Many of these links
are broken, but that is only because git tags have only been added for
some (not all) releases. These tags would need to be added by a
maintainer (not something I can do in a PR).

CHANGELOG.md

@@ -5,7 +5,7 @@ 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/).
 
-## [0.1.18] - 2022-03-30
+## [0.1.18] - 2022-04-30
 
 ### Changed
 
@@ -115,3 +115,17 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Scrollview now shows scrollbars automatically
 - New handler system for messages that doesn't require inheritance
 - Improved traceback handling
+
+
+[0.1.18]: https://github.com/Textualize/textual/compare/v0.1.17...v0.1.18
+[0.1.17]: https://github.com/Textualize/textual/compare/v0.1.16...v0.1.17
+[0.1.16]: https://github.com/Textualize/textual/compare/v0.1.15...v0.1.16
+[0.1.15]: https://github.com/Textualize/textual/compare/v0.1.14...v0.1.15
+[0.1.14]: https://github.com/Textualize/textual/compare/v0.1.13...v0.1.14
+[0.1.13]: https://github.com/Textualize/textual/compare/v0.1.12...v0.1.13
+[0.1.12]: https://github.com/Textualize/textual/compare/v0.1.11...v0.1.12
+[0.1.11]: https://github.com/Textualize/textual/compare/v0.1.10...v0.1.11
+[0.1.10]: https://github.com/Textualize/textual/compare/v0.1.9...v0.1.10
+[0.1.9]: https://github.com/Textualize/textual/compare/v0.1.8...v0.1.9
+[0.1.8]: https://github.com/Textualize/textual/compare/v0.1.7...v0.1.8
+[0.1.7]: https://github.com/Textualize/textual/releases/tag/v0.1.7