code: public Attachment uploadAttachment(String fileName, String contentType,
                                         InputStream content) throws RedmineException, IOException {
          return uploadAttachment(fileName, contentType, content, -1);
      }
docs: Uploads an attachment.
  
  @param fileName
  file name of the attachment.
  @param contentType
  content type of the attachment.
  @param content
  attachment content stream.
  @return attachment content.
  @throws RedmineException if something goes wrong.
  @throws IOException
  if input cannot be read. This exception cannot be thrown yet
  (I am not sure if http client can distinguish "network"
  errors and local errors) but is will be good to distinguish
  reading errors and transport errors.