Release v0.8.0

What's Changed

• Add another example by @michaelsproul in #32
• add flatten by @realbigsean in #34
• Meta variants by @realbigsean in #35
• Fix clippy lints and add CI by @michaelsproul in #37
• Reject multiple attributes on fields by @michaelsproul in #38
• Release v0.8.0 by @michaelsproul in #40

Full Changelog: v0.7.0...v0.8.0