Prepare 2.1 release

Author: XWB

Changelog.md

@@ -1,15 +1,14 @@
 Changelog
 =========
 
-### 3.0.0 (2017-xx-xx)
+### 2.1.0 (2018-03-04)
 
 * Dropped PHP < 5.6 support.
 * Dropped Symfony < 2.7 support.
 * Dropped jQuery < 3 support.
 * Dropped HHVM support.
 * Added Symfony 4 support.
 * Signature of `ThreadPermalinkListener` has been changed.
-* Decrease `Thread::numComments` after comment removal.
 * Route `ThreadController::getThreadsActions` throws 404 if called without id's.
 * Added pipeline parser to integrate several parsers together.
 * Added flat view for async thread.