1. fix a bug test.desc can't be used as identifier, which is valid in mysql 2. introduce ReservedKeyword in parser.y and clean up 3. fix mysql client "use `select`;" can't work 4. refine lexer's special comment mode pos line/offset
1. fix a bug test.desc can't be used as identifier, which is valid in mysql 2. introduce ReservedKeyword in parser.y and clean up 3. fix mysql client "use `select`;" can't work 4. refine lexer's special comment mode pos line/offset