Replace all references to the old n*sleep functions with the equivalent cgsleep_*s replacements.
TimeBeginPeriod and TimeEndPeriod do not add significant overhead when run the entire time for cgminer so avoid trying to maintain balanced numbers of them for specific time calls to simplify code.
Use the reentrant cgsleep functions for usecps in usbutils.
Rename cgsleep_prepare_r as cgtimer_time to get time in cgtimer_t format and call cgsleep_prepare_r as a macro for cgtimer_time
Provide cgtimer_to_ms helper functions.
Provide cgtimer_sub helper functions.
usbutils add cps stats estimates