Add HtmlFlow

[fmcarvalho]

HtmlFlow is a Java DSL to write typesafe HTML documents.

HtmlFlow competes with the most performant template engine, i.e. Rocker and is faster than the remaining concurrency.

HtmlFlow is widely used to build dynamic HTML documents, such as papers, reports, emails, etc, involving complex programing tasks which are hardly achieved through textual templates. Moreover, HtmlFlow can also be used as a web template engine allying its performance boost with its HTML strongly type safety characteristics.