Minor changes in Exercise0.md: changed all the occurrences of 'codeprober.sh' into 'code-prober.sh'. Changed 'localhost:8080' to 'localhost:8000'

Minor changes in README.md: changed all the occurrences of 'codeprober.sh' into 'code-prober.sh'. Changed 'localhost:8080' to 'localhost:8000'

The sources are still in the git history; the removal is purely
to reduce the risk of confusion.