Added changelog

Author: massaru-stark

CHANGELOG.md

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+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
+and this project adheres to the following versioning pattern:
+
+Given a version number MAJOR.MINOR.PATCH, increment:
+
+- MAJOR version when **breaking changes** are introduced;
+- MINOR version when **backwards compatible changes** are introduced;
+- PATCH version when backwards compatible bug **fixes** are implemented.
+
+
+## [Unreleased]
+### Fixed
+- Signature r and s range check
+
+## [1.0.0] - 2020-04-22
+### Added
+- first official version