Refactor MATLAB MEX sources and convert get_header to .m #36

Job	Run time
Build & Test (ubuntu-latest)	8s
Build & Test (macos-latest)	21s
Build & Test (windows-latest)	39s
Build & Test Matlab (macos-latest)	3m 35s
Build & Test Matlab (ubuntu-latest)	1m 50s
Build & Test Matlab (windows-latest)	3m 2s
	9m 35s

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