v0.2.0

Big update! 🎉

• Exun is now using the Zero-Clause BSD License instead of Unlicense
• RawUnexpected and UnexpectedError now have None variants. These aren't string messages, or boxed errors. They're just empty. That means that Options can now be converted into these errors. And since this doesn't require alloc, most features of exun can now be used with just core.
• A new ResultExunExt trait has been created, which extends Result<T, Exun<E, U>>. So it now implements several new methods which should make it more ergonomic
• Many embarassing problems in the docs are now fixed
• Tests no longer fail in no-std
• Exun now implements expect, unwrap_or and unwrap_or_else
• Some methods are now must_use

Added methods:

• Result<T, RawUnexpected>::unexpect
• Result<T, E>::unexpect_none
• Option<T>::unexpect_none
• RawUnexpected::none
• UnexpectedError::none
• Exun::expect
• Result<T, Exun<E, U>>::expected_err
• Result<T, Exun<E, U>>::unexpected_err
• Result<T, Exun<E, U>>::map_expected_err
• Result<T, Exun<E, U>>::map_unexpected_err
• Result<T, Exun<E, U>>::unwrap_result
• Result<T, Exun<E, U>>::unwrap_expected_err
• Result<T, Exun<E, U>>::unwrap_unexpected_err
• Exun::unwrap_or
• Exun::unwrap_or_else