Introduce RDoc::RI::Task
Remove copyright notice /cc
https://github.com/rdoc/rdoc/pull/332#discussion_r20754684
Use '.rdoc' for output dir to work with rdoc-tags /cc
https://github.com/rdoc/rdoc/pull/332#discussion_r20754689
Flatten class /cc
https://github.com/rdoc/rdoc/pull/332#discussion_r20754697
Merge pull request #332 from zzak/ri-task

Introduce RDoc::RI::Task