Improve PDF output styling

[aireilly]

• https://docs.asciidoctor.org/pdf-converter/latest/extend/use-cases/#per-chapter-toc
• https://docs.asciidoctor.org/pdf-converter/latest/extend/use-cases/#theme-admonition-per-type
• https://docs.asciidoctor.org/pdf-converter/latest/extend/use-cases/#language-label-on-code-block
• https://docs.asciidoctor.org/pdf-converter/latest/extend/use-cases/#license-page

Run converters like this:

asciidoctor-pdf -r pdf-converter-admonition-theme-per-type.rb doc.adoc