Importance Matrix calculation (#4861)
* imatrix: 1st version
* imatrix: WIP
* Cleanup
* Update examples/imatrix/imatrix.cpp
Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>
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Co-authored-by: Iwan Kawrakow <iwan.kawrakow@gmail.com>
Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>
