Create extension to detect merge conflicts

[mojavelinux]

Create an extension to detect merge conflicts in AsciiDoc source files.

With large commits, it's easy to miss some conflict and accidentally commit it. Example here:

http://gist.asciidoctor.org/?e4b59c5f6b0a85689859

When this happens in source code, the compiler or a test will normally tell you. If Asciidoctor could detect the pattern and tell you (aka fail the build), that would be great. This could likely be handled by a Preprocessor extension.

[jirutka]

:+1:

[nawroth]

:+1: