C++

Add multm_prev_ layer and enhance gemm() function for PLANE_WISE operations #1324

Job	Run time
ubuntu-20_04-gcc-7	27m 3s
ubuntu-latest-clang-default-avx	29m 15s
ubuntu-latest-ffmpeg7	1m 26s
ubuntu-latest-gcc-11-blas	28m 7s
ubuntu-latest-gcc-default-cmake-3-8-ffmpeg5	25m 51s
windows-2019	14m 41s
windows-latest	25m 58s
	2h 32m 21s

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