Update CHANGELOG for release 2.0.0

Author: ramsey

CHANGELOG.md

@@ -1,5 +1,17 @@
 # Codeblock Extension for Twig Changelog
 
+## 2.0.0
+
+_Released: 2017-04-18_
+
+* Upgrade dependencies to require PHP 5.6 as the minimum PHP version
+* Use [ramsey/pygments](https://github.com/ramsey/pygments) for syntax highlighting with Pygments
+* Quoted strings must now be used for `format` and `lang` attributes
+* Use attributes for `title`, `link`, and `link_text`; stay closer to [Octopress Codeblock](https://github.com/octopress/codeblock)
+* Introduce `class` and drop support for `end` and `range`
+* Remove `phpopentag` attribute and intelligently choose to "start inline" when using Pygments
+* Support extension for Twig 1.15 and up, including Twig 2.0 and up
+
 ## 1.1.0
 
 _Released: 2017-03-28_