variant-1.0.3: changelog.md

## 1.0.3

- Migrated more documentation (EADT, EGADT)

## 1.0.2

- Migrated documentation from the old independent user manual into Haddocks
- Fixed the benchmark
- Added GHC 9.12.4 to CI (9.14.1 is still failing due to dependencies not being
  available)