Add support for asciidoctor-bibtex

[mikeholler]

1. git clone [email protected]:asciidoctor/asciidoctor-bibtex.git
2. Open top-level asciidoctor-bibtex folder in IntelliJ with Asciidoctor IntelliJ plugin installed
3. Open samples/latex_macros_in_bibtex/sample.adoc

Actual:

Expected:

To see all macros and commands added by asciidoctor-bibtex rendered appropriately. Even though this is a plugin, other plugins like asciidoc-mathematical and asciidoctor-diagram have support, and I would love to see the asciidoctor-bibtex plugin get the same love.

My use case is writing technical documentation and designs alongside source code, and I would like to be able to justify my designs with a strong bibliography, but I prefer bibtex and the built-in bibliography is frustrating for handling numbering.

AsciiDoc Plugin Version: v0.23.2

IDE Name and Version: IntelliJ IDEA 2018.3.4 (Ultimate Edition)
Build #IU-183.5429.30, built on January 28, 2019
Licensed to Michael Holler
You have a perpetual fallback license for this version
Subscription is active until February 4, 2020
JRE: 1.8.0_152-release-1343-b26 amd64
JVM: OpenJDK 64-Bit Server VM by JetBrains s.r.o
Linux 4.15.0-45-generic