Play library: implement repetition and halt commands

[oskostenko]

This adds support for repetition () and halt H commands to the Play routine.

@wilco2009, you might probably want to incorporate these changes to your zx81sd port.

[wilco2009]

This adds support for repetition () and halt H commands to the Play routine.

@wilco2009, you might probably want to incorporate these changes to your zx81sd port.

Perfect, thank you. I will implement your new features in the next version.

[oskostenko]

@wilco2009, would it be possible to maintain a single version of the library, with conditional macros?

Something like:

#ifdef ARCH_ZX81SD
  ' zx81sd-specific const values
#elif
  ' default const values
#endif

That way it would be much less pain to maintain multiple architectures.

[wilco2009]

I agree with you, that's the correct way to do it.
If the example is adapted that way, I could remove it from the architecture subfolder since it would simply work without needing to port anything.
I'll do it that way in my next version.