add changelog

Author: Michael Meier

CHANGELOG.md

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+# Changelog
+
+## 0.10.0 - 2018-11-30
+
+### Added
+- Added helper function to access optional properties from elements, return a supplied default value if it hasn't been set
+- Add utility functions to (re-)calculate block format durations
+- Added `adm::ReaderOption` to select `AudioFormatExtended` node search mode
+
+### Changed
+- Use `Catch2` instead of `Boost.Test` for unit testing
+- Refactored XmlParser tests to use separate files for test data
+- Improved search for `AudioFormatExtended` node when parsing XML 
+
+### Fixed
+- Documentation fixes and clarifications 
+- Fixed visibility issues of some methods that prevented linking with the shared library
+
+
+## 0.9.0 - 2018-07-24
+
+Initial release