added explicit VideoWriter::release(). Fixed video stream finalization (write remaining frames); Fixed occasional crash in the case of odd-width or odd-height videos; Fixed a few problems in ffmpeg tests. Positioning still does not work well.

Performance problems fixed. Shared camera buffer is used.

Suppressed hundreds of useless MSVC warnings (can be reenabled setting cmake variable ENABLE_NOISY_WARNINGS to ON). Fixed some of remaining warnings.