code: private Asciidoctor getAsciidoctor() {
          if (asciidoctor == null) {
              asciidoctor = AsciidoctorFactory.getAsciidoctor();
              treeprocessor = new Treeprocessor();
              IgnoreIncludeProcessor includeProcessor = new IgnoreIncludeProcessor();
              JavaExtensionRegistry extensionRegistry = asciidoctor.javaExtensionRegistry();
              extensionRegistry.treeprocessor(treeprocessor);
              extensionRegistry.includeProcessor(includeProcessor);
          }
          return asciidoctor;
      }
docs: Returns an {@link Asciidoctor} instance which is created lazliy to reduce
  startup time.
  
  @return The {@link Asciidoctor} instance.