Suggestion: Allow separating notes of the same frequency

[NY00123]

This issue might seem a bit esoteric, and maybe also get closed, especially with minor differences in audible output between Sopwith 1.5/2 and the Network/Author's Edition.

Right now, as far as I can tell, successive beeps of the same frequency are effectively merged into a single wave. That is, repeatedly calling Speaker_Output with the same frequency (without other calls to the function in-between) is equivalent to making just the very first call.

While this might match DOSBox v0.74 and other variants, I spotted that something with this kind of output was different from vintage hardware quite a while ago. That is exactly what made me implement a fix for Chocolate Doom, and beforehand, even try a similar fix for DOSBox:

chocolate-doom/chocolate-doom#866
chocolate-doom/chocolate-doom#795 (comment)

As I wrote in the PR for Chocolate Doom, the patched behaviors were intended to be closer to specific configurations of DOSBox-X (if not the default), and also to dosbox-staging with pcspeaker=impulse. The change log for the current RC of dosbox-staging v0.82.0 further lists making the impulse PC speaker model the default.

As for sdl-sopwith, the closest approach for such a change that I'm currently aware of is resetting lasttime from the function Speaker_Output. However, while the very beginning of the main theme will indeed sound closer, there are still differences from the DOS versions (with the impulse PC Speaker model). Then again, as mentioned earlier, Sopwith 1.5/2 seems to differ from the Network/Author's Edition a bit here. Question is which DOS sources are available as a reference, in case anyone will want to investigate.