Update version & clean pub.dev

[timbotimbo2]

Description

this plugin and my fork show several issues on pub.dev.

• The :information_source: icon ℹ️, doesn't work in the readme.
• An image in the readme is broken
• The example tab shows lib\example\main.dart, which is useless here.
• Static analysis shows linter errors.

Image:

Static analysis:

This PR

This PR includes:

• Fixes lint warnings in the plugin and example
• Small readme fixes & updates.
• Updates the changelog.
• Adds example.md for the example tab on pub.dev
• Sets the plugin version to 2022.3.0, because WASM supports increases the Flutter & Dart sdk requirements.

Type of Change

• ✨ New feature (non-breaking change which adds functionality)
• 🛠️ Bug fix (non-breaking change which fixes an issue)
• ❌ Breaking change (fix or feature that would cause existing functionality to change)
• 🧹 Code refactor
• ✅ Build configuration change
• 📝 Documentation
• 🗑️ Chore