Handles a string which has just the escape codes
The Bash manual says about escape codes in strings:
Enclosing characters in double quotes preserves the literal value of all characters within the quotes, with the
exception of $, `, \, and, when history expansion is enabled, !. The characters $ and ` retain their special
meaning within double quotes. The backslash retains its special meaning only when followed by one of the fol-
lowing characters: $, `, ", \, or . A double quote may be quoted within double quotes by preceding it
with a backslash. If enabled, history expansion will be performed unless an ! appearing in double quotes is
escaped using a backslash. The backslash preceding the ! is not removed.
THis text preprocessor is used for $'' ASNI escaped strings. The valid escape values are documented at
http://wiki.bash-hackers.org/syntax/quoting .