feat(scripts): robust authors.sh

- Determine the latest two semver release tags by sorting them.
- Dedupe author names using BOTH their e-mail address and their name.
  This ensures that the following two entries dedupe into one.
  - Matias Niemelä (Matias Niemela\xcc\x88)
  - Matias Niemelä (Matias Niemel\xc3\xa4)

Closes #586