support pluggable backends and templates for asciidoctor and other renderers

[lincolnthree]

This could take the form of a folder structure:

.redoculous/
.redoculous/asciidoc/theme/
.redoculous/markdown/theme/

Etc.

[mojavelinux]

To give you an idea of what those templates might look like for AsciiDoc, check out the custom Asciidoctor backends repository:

https://github.com/asciidoctor/asciidoctor-backends

Asciidoctor looks for a template file for each node it visits in the tree and uses the template to produce the backend output, such as HTML, DocBook, etc.

[lincolnthree]

https://github.com/asciidoctor/asciidoctor-backends/

[lincolnthree]

Ah, you beat me! Nice :) Thanks Dan!