Update to v2.0.0

[rurickdev]

This PR has breaking changes

• Use different font files for every stile
• Update generator scripts to use new font files
• [Breaking change] Now to use a particular style you need to use PhosphorIcons.style.icon instead of old PhosphorIcons.iconStyle
• Adds duotone icons support
• Adds new custom widget to render any icons style including duotone
• Update readme:
  • API changes
  • Example of PhosphorIcon widget usage
  • Add new Screenshots
• Upgrade example app
  • Show duotone icons
  • Enable all flutter stable platforms (web, android, ios, linux, windows, macos)
  • Adds linter
• Increment package version to 2.0.0
• Add pub.dev screenshots

[rektdeckard]

This is epic @rurickdev. I've been AFK all day but will spin it up tomorrow just to verify everything's good.

[rektdeckard]

Looks excellent. Nice work with the duocolor effect! Tested locally, and works great.