add parallel_for implementation by pure c++11
add parallel_for implementation by pure c++11

now we can do muti-thread training without intel TBB

zhangqianhui/tiny-cnn,zhangqianhui/tiny-cnn,H4kor/tiny-cnn,H4kor/tiny-cnn,Wangyida/tiny-cnn,Wangyida/tiny-cnn