WIP new release

(DO NOT MERGE)

Preparations for 0.2.1 release. PR needs to be updated with correct dates when we release.
Let's use `FIXME` instead of `TBD` here; the advantages being:

-  we usually use `FIXME` in Python code;
- `pylint` and friends automatically warn people about lines with `FIXME`;
- we'll have a simple unified `git grep FIXME` technique to rely on in order to find all places to fix (regardless of pylint and friends)