Update changelog

CHANGELOG.md

@@ -5,6 +5,24 @@ The format is based on [Keep a Changelog].
 
 [keep a changelog]: https://keepachangelog.com/en/1.0.0/
 
+## 2.0.0
+
+Significant improvements:
+
+* Webserver stays alive as long as there is active TCP traffic, even
+  if there are not new connections being opened. This means Sleeping
+  Beauty works better with long-lasting websockets or HTTP/2 pipes.
+* Various race conditions fixed that could cause deadlocks, dropped
+  connections, or fatal errors.
+* Do not send back an error message when failing to connect to
+  upstream endpoint. While a neat idea to report errors, it does not
+  work well with most protocols built on top of TCP and will cause
+  confusing downstream errors. Instead, the connection is closed
+  immediately without a response when the upstream is not available.
+  This behavior may be improved in future.
+* Errors when proxying traffic are reported in logs. Improved log
+  formatting in general.
+
 ## 1.0.0
 
 Initial release. Configuration options: