Felix19350 2nd submission. Further improved performance by improving the parsing logic

[felix19350]

Further improved performance by improving the parsing logic so that strings for city names are not allocated with each row. Removed JVM options to control heap memory as they are now unnecessary.

Check List:

• [X] Tests pass (./test.sh <username> shows no differences between expected and actual outputs)
• [X] All formatting changes by the build are committed
• [X] Your launch script is named calculate_average_<username>.sh (make sure to match casing of your GH user name) and is executable
• [X] Output matches that of calculate_average_baseline.sh

• Execution time: 0:32.44
• Execution time of reference implementation: 4:03.22

[felix19350]

@gunnarmorling rebased PR as per your request. Sorry about that!

[gunnarmorling]

00:26.500. It fluctuates quite a bit indeed.