extract helper to resolve image icon path for admonition
extract helper to resolve image icon path for admonition

Hextremist/asciidoctor-pdf,asciidoctor/asciidoctor-pdf,mojavelinux/asciidoctor-pdf,asciidoctor/asciidoctor-pdf,dsisnero/asciidoctor-pdf,mojavelinux/asciidoctor-pdf,Hextremist/asciidoctor-pdf,dsisnero/asciidoctor-pdf