Exercise: Parse variable width fields

# In a log file there are rows in which the first 16 and last 16 characters
# describe addresses while everything in between describes several commands
# Each command is built up by a leading character (A, B, C, D, etc) and a number
# of digits. The number of digits depend on the leading character.
# In this example we split up the data to commands and count how many times
# each command type was given.