Added
* Add [tar_contains validator](/docs/validators/tarcontainsvalidator) to validate contents of a tar file
* Add [zip_contains validator](/docs/validators/zipcontainsvalidator) to validate contents of a zip file
* Add [tempfile plugin](/docs/plugins/tempfileplugin) to create temporary files for a test
* Add `init` field for containers. Containers can use it to specify a custom initialization time (default=2)