Update changelog (#290)

Author: dduan

Sources/TOMLDecoder/TOMLDecoder.docc/CHANGELOG.md

@@ -4,6 +4,18 @@ Also known as release notes.
 
 ## In Development
 
+## 0.4.3
+
+Improved runtime performance.
+
+For a TOML document such as [this twitter payload](https://github.com/dduan/TOMLDecoder/blob/cea8f0bee33f37e0fcc33b566a742485c71196e7/Sources/Resources/fixtures/twitter.toml),
+Parsing it costs >50% less CPU instructions,
+and ~100% less memeory retains.
+
+The in release build,
+parsing this document with TOMLDecoder takes less time than the C library [tomlc99](https://github.com/cktan/tomlc99).
+
+
 ## 0.4.2
 
 - Fixed a project configuration that prevented SwiftPM consumption of the package