Add start and end column to Annotation (google#1241)

Update git_refs.go (google#1240)

Support go1.13 (google#1279)

Closes google#1273.

Add missing fields to PullRequest: locked and rebaseable (google#1269)

Fixes google#1264.

Bump major version to v28 due to google#1238

Add missing `CreatedAt` field in users_keys class (google#1256)

Fixes google#1255.

Add PullsURL to PushEventRepository (google#1253)

Fix GetProjectCard argument name (google#1239)

Use time.Until (google#1233)

Add support for creating and using template repos (google#1236)

Fixes google#1235.