This module provides a single function, 'tty_length', which returns the
length of a string excluding any ANSI tty / terminal escape codes. I.e. the
number of characters that will appear on screen. This is useful if you're
working out the width of columns, or aligning text.

tty_length( STRING )
Takes a single string, and returns the length of the string, excluding
any escape sequences.

Note: the escape sequences could include cursor movement, so the length
returned by this function might not be the number of characters that
would be visible on screen. But
'length_of_string_excluding_escape_sequences()' was just too long.