Add support for Screen Text and Italics
Add preamble handler

The text gets embedded, but somehow is not visible. But, it's good enough for the moment, since this part isn't needed to Packt.
Added Gradle file to ignored file list.
Sample Gradle build file with Asciidoctor plugin.
Renamed build.gradle to asciidoc.gradle
Merge remote-tracking branch 'upstream/master'

Keep up-to-date with original repository.