2.0.0-nullsafety.0 - Jan 20, 2021

• Migrate this package to null safety.
• Sdk constraints: >=2.12.0-0 <3.0.0 based on beta release guidelines.
• Depends on flutter_provider package.
  So bloc will be created lazy i.e. on the first access.
• Added extension BuildContext.bloc<T>({bool listen = false}). It is identical with BlocProvider<T>.of(BuildContext, {bool listen = false}).
• Changed signature of builder in RxStreamBuilder(builder: ) constructor to Widget Function(BuildContext, T?).
  Previous signature is Widget Function(BuildContext, AsyncSnapshot<T>).
• Fixed many issues.
• Many improvements.