Release plan for 0.8

[Schönberger Johannes]

I think we should push the release some days back to fix the majority of these issues.


> https://github.com/scikit-image/scikit-image/issues/318

I'll take on this tomorrow.

> https://github.com/scikit-image/scikit-image/issues/336

Made the necessary changes today as part of a new PR.

> https://github.com/scikit-image/scikit-image/issues/341

I commented on this topic on github.

> https://github.com/scikit-image/scikit-image/issues/418 (check relevance)

Has been fixed before, so closed.