Changes since last release:
- Chapter 2, step F: You can now start more than one vehicle at the same time.
- Chapter 2, step F: Removed backward travel.
- Chapter 2, step H: Added explanatory text about public stops.
- Chapter 3, step C: Bridge construction now replaced by tunnel construction.
- Fix (more) issues when building a tunnel.
- Add jump_to_link_executed function.
- Code and text cleaning.
- Minor improvements and bug fixes.