C++

Add multm_prev_ layer and enhance gemm() function for PLANE_WISE operations #1321

Job	Run time
ubuntu-20_04-gcc-7	27m 0s
ubuntu-latest-gcc-11-blas	26m 57s
ubuntu-latest-ffmpeg7	1m 17s
ubuntu-latest-clang-default-avx	29m 5s
windows-2019	15m 35s
ubuntu-latest-gcc-default-cmake-3-8-ffmpeg5	26m 3s
windows-latest	24m 9s
	2h 30m 6s

Provide feedback