Intepreter for the pseudocode used in the school-level selection of the Olympiads in Informatics

For the 2022/2023 edition, we updated the pseudocode that has been in use since 2018 in the school-level selections, making it more expressive and potentially suitable for other competitions as well. We're also working on an intepreter for the pseudocode, to ease debugging and work as a stepping stone towards more complex programming languages.