25us is far too small, and would result in std::this_thread::sleep_for
being called with this as a maximum value. This means that a guest
application that produces frames instantly would only be limited to
40 kHz.
25ms is a more appropriate value, as it allows for a 60 Hz refresh
rate while providing enough slack in the negative region.
Now based on std::chrono, and also works in terms of emulated time
instead of frames, so we can in the future frame-limit even when the
display is disabled, etc.
The frame limiter can also be enabled along with v-sync now, which
should be useful for those with displays running at more than 60 Hz.
MerryMage