New release note process

To make sure we have (1) have a nice list of release note changes, (2) we do not forget to add contributions in the release notes, I suggest to incrementally build the release notes with each PR. E.g., similar to the dev process in NumPy or scikit-learn.
Hm, are we already sure it's going to be called 0.11.0 or is that always clear in advance e.g. 0.11.1 vs. 0.12.0 etc.? That's the motivation behind "dev". But I am also fine with your way...