Extend YAML parsing with dynamic & flattened vars

[briandominick]

The way @mojavelinux has extended YAML parsing in the asciidoctor-pdf gem is pretty amazing. The code is here and the DSL documentation is here. This is a really simple and elegant enhancement. It lets you build cumulative variable values and it enables unique, flattened variables formed from the nested structure.

domain: codewriting.org
uri:
  base: http://$domain
  base_ssl: https://$domain
  blog: $uri_base_ssl/blog

Which can then produce variables that are called as such in AsciiDoc: {uri_blog}.

This should probably be a module inside LiquiDoc until it's ready to stand on its own, then maybe spin off its own gem to share this functionality more broadly.

[mojavelinux]

For how sophisticated YAML is, I'm surprised something like this isn't built in.