First docgen integration.

Signed-off-by: Julien Viet <julien@julienviet.com>
Annotate the examples package with @Source instead of each example class
Have the asciidoc generated files in the src/main/asciidoc
Change extension to ".ad" instead of ".adoc"

Signed-off-by: Julien Viet <julien@julienviet.com>
Merge pull request #977 from eclipse/docgen

First docgen integration.