We implement nanotime by converting QueryPerformanceTimer output with
floating point arithmetic. This is necessary to preserve precision on
platforms where each tick is not an integer number of nanoseconds.
Furthermore, struct timespec is included C11 and appears to be supported
on Windows, so we no longer need to #ifdef it out.
This makes it a compile-time error to call a function that semantically
takes no parameters with a nonzero number of arguments.
Previously, such code would still compile, but risk blowing up the stack
if a compiler chose to use something other than caller-cleanup calling
conventions.
