* Added virtual qualifier to a few destructors in subclasses.
* Removed a few empty destructors that didn't need to be explicitly defined.
* Fixed a few typos
* Removed unnecessary empty virtual destructors in some classes with parent's who derrived from a class with a virtual destructor
The demo relied on the build context returning accumulated times in
microseconds. On Windows this was using QueryPerformanceCounter directly
which has a higher resolution, thus returning wrong measured times. We
now report the accumulated times in microseconds on all platforms.