[ci skip] Prepare release 0.21

Merge pull request rusqlite#551 from gwenn/0.20.0

[ci skip] Prepare release 0.20

[ci skip] Prepare release 0.19

rusqlite 0.19.0
And libsqlite3-sys 0.15.0

Prepare 0.14.0 release

[ci skip] Prepare version 0.17.0

[ci skip] Prepare 0.16.0 release

[ci skip] prepare version 0.15.0

[ci skip] Prepare 0.14.0

Bump to v0.13.0.

Merge pull request rusqlite#281 from jgallagher/publish-0.12.0

Bump to 0.12.0