replaced usleep for windows

New: changed 2000 into a constant defined inline

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- Added functions to test usleep, msleep and sleep for accuracy. 
- Replaced windows usleep version with a non busy waiting high accuracy Version.
- Modified CALLBACK_ACCELERATOR_RATIO for windows because some systems need larger input buffer to work fine.

There are still issues when the framerate drops but that will be another worklist item ...

... done.