The function is made safe and now returns Result. Functionally it now
fails when it can not write the newly generated key to the database
whereas before it still returned the key but logged a warning. There
is no reason this shouldn't be able to store the key and silently not
storing the key may result in later operations assuming the key is
available, so failing seems like a better choice.
The function now also uses a proper mutex to guard against multiple
threads generating keys. And this mutex is Context-scoped rather than
fully global (static).
* chore: update some ci
* feat: no more libiconv
* refactor: updates for updated mmime api
* fixup: correct mmime path
* cleanup
* use newer visual studio
* Update appveyor.yml
* unify libc imports and improve windows situation
* refactor: use rust based sleep
* improve cross platform state of types
* docs: update readme badges
