Release 0.8.0 for Flutter null safety

Merge pull request #22 from ChangJoo-Park/0.8.0-nullsafety.0

0.8.0 nullsafety.0

Release 0.6.0

Remove authors from pubspec.yaml

Chronometer

• Support Chronometer

Decorative

You can using icon, title, content, subtext from this version.

just work

0.0.1

Update README.md