eventify

• Resolved lint error with updated lint options.

• Migrated to null-safety. This package is compatible with null-safety.
• Resolved observation from linting tool.

• Resolved observations in pub.
• Resolved issues with the cancelation of events.cancel property is now changed to method, to make it consistent with the older implementation, signture of the same is kept as-is.
• Updated library documentation.

• Performance optimization - Observed that in real-time applications, removing event handlers were taking lots of time. Same observed with adding handlers also.
• Modified code to use Set, instead of list to provide faster performance.
• Removed unwanted checks while adding handlers.

• Addressed health and maintenance suggestions.

• Added additional examples.

• Removing event registration in the callback caused exception. Addressed the issue by creating a sublist and triggering callback from there.

• Added example.dart

First reviewed version.