Simulate most popular Apple II system clock

[mobluse]

I think JSBASIC should support a real time clock, e.g. one that is supported in popular Apple II emulators, see https://en.wikipedia.org/wiki/Apple_II_system_clocks. "When the Thunderware Thunderclock Plus was released in 1980, it quickly became the de facto standard for an Apple II system clock. When Apple Computer released its new ProDOS operating system in 1984, a Thunderclock software driver came built-in. From that point on, all new Apple II system clocks strived to emulate the Thunderclock." The emulator AppleWin seems to support the Thunderclock card.

The clock could be set to current local time by default.

This could solve the problem with games running at different speeds on different computers, and also make it possible to run games both on JSBASIC and on real Apple II with system clock, see https://github.com/inexorabletash/jsbasic/issues/20.

I could play this Tetris game in JS by inserting a delay loop on line 350 that counts to 2000 in my case, but that could have been configured automatically if we had a real time clock in JSBASIC.