void add(int c) {
            if (prevC + 1 == c) {
                // in range
            } else {
                flushRange();
                fromC = c;
            }
            prevC = c;
        }
Removes leading and trailing quotation mark from the given string. This method will properly unescape whatever
content is withing the string literal as well.

@param str The string to unquote.
@return The unquoted string.
vespajlib/src/main/java/com/yahoo/javacc/UnicodeUtilities.java