Fixing config option "retained_stages" => "retainedStages".

This is a very esoteric option and it's out of sync with the style we use.
So it seems fitting to fix it for 0.9.0.
Merge pull request #364 from pwendell/fix

Fixing config option "retained_stages" => "retainedStages".

This is a very esoteric option and it's out of sync with the style we use.
So it seems fitting to fix it for 0.9.0.