Create a function that returns the selected filename from a path including the file extension.
getFilename("C:/Projects/pil_tests/ascii/edabit.txt") ➞ "edabit.txt"
getFilename("C:/Users/johnsmith/Music/Beethoven_5.mp3") ➞ "Beethoven_5.mp3"
getFilename("ffprobe.exe") ➞ "ffprobe.exe"