River Raid Rust: merging more PRs and breaking the program into different modules
This is kind of long and focused on merging the PRs we've got, including a PR to break the program in different modules. Other PRs are:
- preventing bullets from passing through land
- updated README.md
- show the cause of "end game"
- show ascii art only if the screensize is enough
- show pause box
- breaking the project in different modules