• Add Canvas view
• Made TextView easier to use when appending content
  • Added TextView::append_content()
  • Added ScrollStrategy to control scroll behavior on content change.
• Made Menubar easier to use with dynamic content
  • Added methods to clear and edit menu trees
• Add "real" fullscreen views to StackView
• Rename View::get_min_size -> View::required_size
• Fix off-by-1 error in termion backend