code: public BinaryString trim(BinaryString trimStr) {
  		if (trimStr == null) {
  			return null;
  		}
  		return trimLeft(trimStr).trimRight(trimStr);
  	}
docs: Walk each character of current string from both ends, remove the character if it
  is in trim string.
  Return the new substring which both ends trim characters have been removed.
  
  @param trimStr the trim string
  @return A subString which both ends trim characters have been removed.