**Filtering**
- [x] do not expose Opts as public
- [x] create separate config/spec for existing, stable options that should be accessible from the outside
- [x] head and tail should be fixed, not exposed
- [x] build filter from payload filter opts
**Selection**
Merge old (rand) and new (complete) selection algorithms into one, based on the new algorithm (with options to use one or the other)**
- [x] Remove `RandOpt`
- [x] Rand selection needs its own `SelectNext`
- [x] NewSelector function to used an existing (completed) selector as input (i.e., using the pre-existing selector's selection stats as a starting point)
- [ ] For the rand selection: options to set number of base iterations + number of iterations without improvement
**API **
- [ ] Facilitate different runs with different scoring functions (in sequence or as separate batches)
- [ ] New feat cats for demo (internal issue https://github.com/stts-se/manuscriptor2000/issues/29)