Bintray & Asciidoctor

Cleaned up a lot of build.gradle

- Publish to Bintray 
- Publish snapshots to oss.jfrog.org
- Allow for signing on Bintray
- Allow for sync to Maven Central
- Use Gradle 2.1 plugin layout
- Killed off Codehaus
- Asciidoctor upgraded to latest version
- Asciidoctor can also build PDF now

For Bintray you'll need to
- Create a GPars organisation
- Create a GPars repo
- Once published, link to JCenter
- Once published, request uploading snapshots to oss.jfrog.org
- Create a signing key