Uses Still.Compiler.TemplateHelpers.ContentTag to render an anchor tag.

Requires a :to option, the target URL. If this is a relative path, the website's base URL is prepended. If it is an absolute path the target: "_blank" and rel: "noopener noreferrer" options are added to be passed to Still.Compiler.TemplateHelpers.ContentTag render function.

If there is a do block, it uses the current file preprocessor to render markup. Note that this is on demand, outside Still.Compiler.CompilationStage.