V2.1.Beta03: ChangeLog: date the Beta3 entry and add the demo and example changes

• The project has now moved to Beta3 state. In a week or so, if no blocking issues arise, this will become the official, stable BASIC256 v2.1
• Whole numbers are the full 64 bits on every platform: the bitwise shift operators (<< and >>) , reading a large whole number from a string or with INPUT and an error on too large numbers now work on all architectures.
• The Edit and Text Output windows now follow a colour theme, chosen from View/Theme: Follow System (the default), Light, or Dark. The Graphics Output window is not themed and stays white, so existing programs draw exactly as before.
• The About box, Help/Online help and F1 keyword help now open https://doc.basic256.org, which serves the same documentation site under its own name.
• Help/Check for update now simply opens the GitHub releases page, https://github.com/uglymike17/basic256/releases, where the builds for every platform are published. Compare the version there with the one in Help/About BASIC-256.
• Browser (WASM): sound and speech work on iPad and iPhone, started by the first touch anywhere on the page.
• Browser (WASM): the demos that expected a keyboard can be driven with a finger. BubbleUniverse_variations starts on a tap and cycles its variations on a tap or a click, StrangeAttractors is explored by dragging and cleared with a double-tap, and AIChatbot fills the window instead of sharing it with the editor.
• Examples: PacMan has been reworked -- a fixed 50 frames a second, a score that carries across lives, and the playfield narrowed so the score and legend have a panel of their own. A new game, Claude-AI-neon_snake, has been added.