Update version to 0.3.0

Author: Dekker1

CHANGELOG.rst

@@ -9,6 +9,9 @@ this project adheres to `Semantic Versioning <https://semver.org/>`_.
 Unreleased_
 ------------
 
+0.3.0_ - 2020-07-21
+-------------------
+
 Added
 ^^^^^
 - Add support for different MiniZinc compiler optimisation levels. All methods that
@@ -137,6 +140,7 @@ release is best described in the `documentation
 <https://minizinc-python.readthedocs.io/en/0.1.0/>`_.
 
 
+..  _0.3.0: https://gitlab.com/minizinc/minizinc-python/compare/0.2.3...0.3.0
 ..  _0.2.3: https://gitlab.com/minizinc/minizinc-python/compare/0.2.2...0.2.3
 ..  _0.2.2: https://gitlab.com/minizinc/minizinc-python/compare/0.2.1...0.2.2
 ..  _0.2.1: https://gitlab.com/minizinc/minizinc-python/compare/0.2.0...0.2.1