Merge pull request PyO3#690 from PyO3/v0.8.4

Bump version to 0.8.4

Merge pull request PyO3#674 from PyO3/v0.8.3

V0.8.3 amend

Merge pull request PyO3#650 from PyO3/v0.8.2

Bump version to 0.8.2

Merge pull request PyO3#616 from PyO3/v0.8.1

Bump version to 0.8.1

Merge pull request PyO3#485 from PyO3/release_0_7_0

Release 0.7.0

(cargo-release) pyo3-derive-backend- version 0.6.0