privat/nit — pull request #695 by xymus (2014-08-28 16:09:40+00:00)
Title: nitdoc: cache `concern_rank`

Improve performance of nitdoc by 60 times in some cases!

Fixes #692, nitdoc on RnR goes from 8 min to 7 sec.

Signed-off-by: Alexis Laferrière