code: public static String subPath(String dirPath, String filePath) {
  		if (StrUtil.isNotEmpty(dirPath) && StrUtil.isNotEmpty(filePath)) {
  
  			dirPath = StrUtil.removeSuffix(normalize(dirPath), "/");
  			filePath = normalize(filePath);
  
  			final String result = StrUtil.removePrefixIgnoreCase(filePath, dirPath);
  			return StrUtil.removePrefix(result, "/");
  		}
  		return filePath;
  	}
docs: 获得相对子路径，忽略大小写
  
  栗子：
  
  <pre>
  dirPath: d:/aaa/bbb    filePath: d:/aaa/bbb/ccc     =》    ccc
  dirPath: d:/Aaa/bbb    filePath: d:/aaa/bbb/ccc.txt     =》    ccc.txt
  dirPath: d:/Aaa/bbb    filePath: d:/aaa/bbb/     =》    ""
  </pre>
  
  @param dirPath 父路径
  @param filePath 文件路径
  @return 相对子路径