Allow antora:antora goal to be used without a project
Since the antora:antora goal is self contained, it should be possible to run it output of a Maven project (no POM file). In order to allow this, the following changes need to be made:
- set requiresProject = false on the mojo class
- resolve basedir to the current working directory when no project is present
- don't set the to-dir option by default (since this is done primarily to conform to a Maven project)
With those changes, it's possible to run the plugin as follows:
mvn org.antora:antora-maven-plugin:antora
Configuration can be provided by way of user properties. For example:
mvn org.antora:antora-maven-plugin:antora -Dantora.playbook=author-antora-playbook.yml