add support for `\b`

src/lexer.cpp

@@ -235,6 +235,7 @@ static bool is_unicode_Lo_char(uint32_t c) {
                     case 'n':  buff.push_back('\n'); break;
                     case 'r':  buff.push_back('\r'); break;
                     case 't':  buff.push_back('\t'); break;
+                    case 'b':  buff.push_back('\b'); break;
                     case 'x': {
                         char hex[3] = {eatchar(), eatchar(), '\0'};
                         size_t parsed;

src/str.cpp

@@ -260,6 +260,7 @@ int utf8len(unsigned char c, bool suppress){
                 case '\n': ss << "\\n"; break;
                 case '\r': ss << "\\r"; break;
                 case '\t': ss << "\\t"; break;
+                case '\b': ss << "\\b"; break;
                 default:
                     if ('\x00' <= c && c <= '\x1f') {
                         ss << "\\x"; // << std::hex << std::setw(2) << std::setfill('0') << (int)c;