Asciidoctor's standard include::[] processor reimplemented as an extension

 This is a reimplementation of the Asciidoctor's built-in (pre)processor for the
 include::[] directive in extensible and more clean way. It provides the same
 features, but you can easily adjust it or extend for your needs. For example,
 you can change how it loads included files or add another ways how to select
 portions of the document to include.