Data-Science Code Review

Joe,
I forked level_up_exercises and imported solutions that I had been placing in a different project. Going forward I will use this fork to submit pull-requests.

Zamir
Use `self.is_valid_file?` instead of `DinosaurCSVParser.is_valid_file?`.<br>Use def with parentheses when there are parameters.<br>Rename `is_valid_file?` to `valid_file?`.