New custom element feature that allows to define HtmlFlow views such as the listing at the end of this post (this feature applies regardless being a static or a dynamic view).

This sample is available on unit tests htmlflow.test.views.HtmlCustomElements

Invoking .custom("alert-info") returns an instance of a new class CustomElement that inherits from existing Div class. Hence, we have most HTML features available at the resulting instance.

Solves https://github.com/xmlet/HtmlFlow/pull/80

StaticHtml
  .view()
      .html()
          .head()
              .script()
                  .attrSrc("alert.js") // Link to alert-info definition
                  .attrDefer(true)
              .__()
          .__()
          .body()
              .div()
                  .attrClass("container")
                  .p().text("Testing custom elements!").__()
                  .custom("alert-info") // alert-info should be stored in the new Element and accessible to the Visitor.
                      .addAttr("title", "Information")
                      .addAttr("message", "This is a message for a custom element")
                      .addAttr("kind", "success")
                      .ul()
                          .li().text("For any reason we could even include other elements.").__()
                      .__() // ul
                  .__() // alert-info
              .__() // div
          .__() // body
      .__(); //html