Add bibliography support

[giflw]

There is a gem to add bibliography: https://github.com/riboseinc/asciidoctor-bibliography

Would be nice to have it available on the default installation of AsciiDocFX.

[daacosta]

Yes... This is needed badly. If Asciidocfx can use this it will become the monster that I need:

1. Bibliography with support for csl standard
2. BibTex support for styles and the ability to read and use bib files
3. Cross-references