C++

Add multm_prev_ layer and enhance gemm() function for PLANE_WISE operations #1320

Job	Run time
ubuntu-20_04-gcc-7	27m 29s
ubuntu-latest-clang-default-avx	28m 44s
ubuntu-latest-ffmpeg7	1m 21s
ubuntu-latest-gcc-11-blas	26m 53s
ubuntu-latest-gcc-default-cmake-3-8-ffmpeg5	25m 49s
windows-2019	15m 53s
windows-latest	26m 18s
	2h 32m 27s

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