Markdown and ShaderMask controls

[FeodorFitsner]

What's new

• Support Flet Viewer in WSL #153
• File structure of "assets" directory should not be cached #149
• Update all Flet icons #151
• Image properties:
  • src_base64 - displays an image from base64-encoded string
• New Page methods:
  • launch_url(url) - opens url in a new browser window
• New Markdown control:
  • value
  • extension_set: none (default), commonMark, gitHubWeb, gitHubFlavored.
  • selectable
  • on_tap_link
• New ShaderMask control:
  • content
  • blend_mode - https://api.flutter.dev/flutter/dart-ui/BlendMode.html
  • shader - see Container.gradient
• New Container event handlers:
  • on_hover

import flet
from flet import Container, Page

def main(page: Page):
    def on_hover(e):
        e.control.bgcolor = "blue" if e.data == "true" else "red"
        e.control.update()

    page.add(
        Container(width=100, height=100, bgcolor="red", ink=False, on_hover=on_hover)
    )

flet.app(target=main)

Fixed bugs

• Bug: setting page.window_width/window_height not working on OSX  #119