speedup by multi-core cpu parallel processing

[erspicu_brox]

6x is too heavy.fps is less than 60.
I add parallel processing for scaler , but it's c# version code.
I think C++ is also ok by this way.
from my pc , 6x sometime less than 50 fps , but now it's 130 up fps.

http://paste.ofcode.org/g7sDMGEaJPHXHSUhd96wmN
hope it's useful for some old pc.

[Zenju]

xBRZ can already be (and should be) used in parallel as is. No need for a rewrite.