Create separator characters
apply edit distance functions on strings split on newlines so that there are no memory issues
separators used to highlight differences. If sep is empty, then no separator is used. If sep contains one character, it is taken as the unique separator. If sep contains 2 or more characters, the first half of the characters are taken as opening separator and the second half as closing separator.
a (String, String) displaying the differences between each input strings. The used separators are specified by the caller. The string is shortened before and after differences if necessary.