allow latest file, update to latest dart_flutter_team_lints (#78)

This unblocks the dependency cycle so that the latest package:file can work with package:test.

Also preps to release.

rev version in prep. for publishing (#65)

* rev version in prep. for publishing

* Update CHANGELOG.md

Prepare to publish (#61)

Fix README example missing import (#51)

Fixes #50

Update to stable SDK and dev deps, add testing on the oldest supported
SDK.

stable null safety release (#47)

release 2.0.0-nullsafety.0 (#45)