Add undo toast

SwiftToast 0.1.0
This release introduces a dedicated undo toast and improves the example app.
What’s new

Added ToastType.undo with:
Countdown indicator
Custom undo action
Added the reusable CountdownView component.
Updated the example app with an undo-toast demonstration.
Fixed running the example app in the iOS Simulator.
Expanded the README with undo-toast documentation and examples.

MVP

0.0.7

Release 0.0.7