lifecycle 0.2.0

Lifecycle support for Flutter widgets.

[0.2.0] - 2021/04/12.

• null safety.

[0.1.1+1] - 2020/12/30.

• Fix a NPE caused by debug log.

[0.1.0] - 2020/12/21.

• Emit push after initState and pop before dispose.
• Optimize events delivery in nested page view.

[0.0.6] - 2020/10/28.

• Bug fix.

[0.0.5] - 2020/10/15.

• Support usage of Navigator widget.

[0.0.4] - 2020/09/27.

• Remove the active event which sent manually after page view pushed.

[0.0.3] - 2020/09/24.

• Fix bugs in nested page view.

[0.0.2] - 2020/09/23.

• Support nested page view.

[0.0.1] - 2020/09/23.

• Initial release.