added changelog

Author: Romain MONTAGNÉ

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 [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [Unreleased]
+
+## [v0.2.0] - 07/06/2020
+
+### Added
+
+- Mixed fleet option
+- Greedy randomized pricing option
+- Stabilization with Interior Points
+- Diving heuristic WIP
+
+### Changed
+
+- Pricing strategy names