0.3.0

• Add only_if evaluator for successful or redirect (2xx, 3xx) responses (#7)
• Support Vary-headers (#6)
• Improve instantiation of callbacks and registry provider
• BREAKING: Simplify instantiation and hooking into flask response handling (#8)
  • No more need to instantiate FlaskCacheControl for Flask app.
• BREAKING: Drop support for only_if=None
  • Use more explicit only_if=Always instead
• BREAKING: Restructure modules
  • Direct imports from modules inside the package need to be adapted.
• Improve test structuring
• Fix flask instantiation and import in example