Added changelog (#61)

Author: Nyholm

Changelog.md

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+# Change Log
+
+The change log describes what is "Added", "Removed", "Changed" or "Fixed" between each release. 
+
+## UNRELEASED
+
+## 0.4.2
+
+### Added
+
+* A KeyNormalizer that cleans the cache keys from invalid chars.
+
+### Fixed
+
+* Exception when clearing cache with a non taggable pool
+* Default value for the second argument to `RecordingCachePool::timeCall` should be array, not null. 
+
+## 0.4.1
+
+No changelog before this version