code: public static void addCustomSupportType(Class<?> clazz, XsonWriter writer, XsonReader reader) throws XsonException {
  		if (null == clazz) {
  			throw new XsonException("clazz Can not be null");
  		}
  		if (null == writer && null == reader) {
  			throw new XsonException("Writer and Reader Can not be null");
  		}
  		if (XsonConst.WRITER_MAP.containsKey(clazz)) {
  			throw new XsonException("Writer already exists: " + clazz.getName());
  		}
  		if (XsonConst.USER_READER_MAP.containsKey(clazz)) {
  			throw new XsonException("Reader already exists: " + clazz.getName());
  		}
  		XsonConst.WRITER_MAP.put(clazz, writer);
  		XsonConst.USER_READER_MAP.put(clazz, reader);
  	}
docs: 添加用户自定义的Reader和Writer