core:time - Added stopwatch procs to return the duration in relevant procedures. Added naming suggestion.

[DragosPopse]

time.stopwatch_stop, time.stopwatch_reset now return the duration they ran for. This is to reduce the need of this common pattern

// BEFORE
time.stopwatch_start(&sw)
duration := time.stopwatch_duration(sw)
// This working differently than _stop, it could be incorrectly placed before the duration get
time.stopwatch_reset(&sw)

// AFTER
time.stopwatch_start(&sw)
duration := time.stopwatch_stop(&sw) // This can also be replaced by a _reset

There is another small naming convention suggestion later down the file. I'm not much attached to that particular change but i figured it wouldn't be bad to unify the procedure names between Duration and Time, plus it's much terser to write when you are working a lot with time.