This is a mandatory release checklist.

- select a version string with pattern `v<major>.<minor>.<patch>` optionally
  with a `-pre<count>` suffix (e.g. `v1.2.45-pre67`)
- reserve resistor combination in `pcb/versions.tsv` by adding version string
- set values of `R1` and `R2` in root schematic according to `pcb/versions.tsv`
- write version string to PCB silk screen
- commit all changes
- execute all automated and manual tests
- create release tag