code: public DelimitedStringParser extractInteger(String key, Consumer<Integer> consumer) {
          this.extractors.put(key, new Extractor<>(consumer, Integer::parseInt));
          return this;
      }
docs: Associates the given consumer with the given key. This consumer will be invoked every time a Key-Value pair with
  the given key is encountered (argument is the Value of the pair). Note that this may be invoked multiple times or
  not at all, based on the given input.
  
  @param key      The key for which to invoke the consumer.
  @param consumer The consumer to invoke.
  @return This object instance.