Proposed new maven site extension

[rafabene]

Maven can generate html sites with reports like javadoc, xref source, plugin usage, etc.

It should be fine that awestruct could generate and use the entire generated site.

One example can be found here: https://site-jdf.rhcloud.com/quickstarts/qstools/target/site/ that was generated using this 'ad hoc' extension: https://github.com/rafabene/jdf-site/blob/JDF-242/_ext/maven.rb

It shoud work in conjunction with indexifier so these pages will have inhibit_indexifier=true.
Once the maven site is generated, it could be cached at _tmp

[rafabene]

Use a awestruct layout is desired but not mandatory for now.

[rafabene]

Initial implementation: https://github.com/jboss-jdf/jdf-site/blob/master/_ext/maven.rb