Tag 0.18.1 release.

Tag 0.18.0 release.

Tag 0.17.0 release.

Prepare 0.16.1 release.

Merge pull request googleapis#1854 from daspecster/cut-0.16.0

Update to version 0.16.0

Merge pull request googleapis#1842 from dhermes/cut-0.14.1

Cut 0.15.0 release.

Tag 0.14.0 release.

Merge pull request googleapis#1740 from dhermes/cut-0.13.0

Upgrading version to 0.13.0.

Merge pull request googleapis#1725 from daspecster/cut-0.12.1

Upgrading version to 0.12.1

Merge pull request googleapis#1689 from dhermes/cut-0.12.0

Upgrading version to 0.12.0