Release 0.6.0

[vincent-herlemont]

• [x] https://github.com/vincent-herlemont/native_db/issues/82
• [x] Rust 2021
• [x] https://github.com/vincent-herlemont/native_db/pull/89
• [x] Auto-migration from 0.5.x to 0.6.0 because is breaking.