Extension to enable SelfPipeline, to configure a Markdown parsing/convertion to HTML automatically
from an embedded special tag in the input text <!--markdig:extensions--> where extensions is a string
that specifies the extensions to use for the pipeline as exposed by Configure(Markdig.MarkdownPipelineBuilder, System.String) extension method
on the MarkdownPipelineBuilder. This extension will invalidate all other extensions and will override them.