Even with USE=doc, the tutorials directory is not installed.
The files from the doc directory are missing, too.
Created attachment 88109 [details, diff] Patch to properly install documentation This patch modifies the ebuild to install documentation from directory doc unconditionally and the tutorials if USE=doc has been set.
BTW, no need to install INSTALL and COPYING...
Created attachment 88119 [details, diff] Adjusted patch to include changes mentioned in comment #3
Please note that even with my patch the ebuild does NOT install the API documentation since that's currently broken upstream (and the fix is not obvious).
fixed in 2.1.4