V1.2.0 changes

See merge request !110

Bump the package version from 1.1.3 to 1.2.0 in setup.py. Update the changelog with new features, including single-agent reinforcement learning, layout thumbnails, and sequence diagrams for internal execution flow.

Added Christoph Kowalski to AUTHORS.md and README.md. Removed Annika Österdiekhoff and Dominik Battefeld from setup.py author list. Updated CHANGELOG.md with new RL feature and cleaned up README.md formatting.

SB3 RL with Hydra

See merge request !109