Prepare to release new version

- Bump CHANGELOG.md
- Use ruff and coverage instead of pylint and test in release rule

Expressions and augmented expressions

Support simple operations like `variable = expression` and `variable +=
expression` which store their result in a separate property. Disabled by
default, enable via constructor or a property of the parser. Variable
scope can now be replaced as well. Use this to keep a context in the
interpreter as demonstration.

Update README and unit tests.

Track which variables are used in the expression

Improve unit test coverage

Update README