code: public static void putKey(Writer writer, String key) throws IOException {
  		writer.write("\"");
  		writer.write(sanitize(key));
  		writer.write("\":");
  	}
docs: Writes the given key as a JSON hash key, sanitizing with {@link #sanitize(String)} as a valid JSON-formatted data.
  @param writer {@link Writer} to be used for writing value
  @param key Keyの文字列表現
  @throws IOException
  @author vvakame