1.0.0-alpha.12

Breaking Changes

• Remove RefreshTokenFields and related type parameters (unnecessary since 9152d3f)
• Add either an Extension variant or #[non_exhaustive] to all exported enums; this raises the minimum supported Rust version to 1.40 but should reduce future breaking changes related to enums

Other Changes

• Update to oauth2 3.0.0-alpha.9, which includes reqwest 0.10 when the reqwest-010 feature flag is enabled
• Add CoreAuthErrorResponseType enum