Doc live edit

It appears to support this we need to use the --watchdir attribute as described in https://github.com/guard/guard/issues/53

The changes for this Pull Request

* Ensure the buildDir is created and that the images are copied over to the buildDir (i.e. if you have never run gradlew asciidoctor or have cleaned the build directory)
*  Provides a guard.sh file for easily executing guard with the proper --watchdir arguments

NOTE: I haven't updated the CONTRIBUTING-DOCUMENTATION.md file