3.5.12 `kr-string' - emit string for K&R C

Usage: (kr-string string)
Reform a string so that, when printed, a K&R C compiler will be able to compile the data and construct a string that contains exactly what the current string contains. Many non-printing characters are replaced with escape sequences. New-lines are replaced with a backslash-n-backslash and newline sequence,

Arguments:
string - string to reformat