consume PX4/Matrix repository and preserve history

src/lib/matrix/.gitignore

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+*.orig
+*.swp
+*~
+astyle/
+build*/
+cmake_install.cmake
+CMakeCache.txt
+CMakeFiles/
+compile_commands.json
+CPackConfig.cmake
+CPackSourceConfig.cmake
+CTestTestfile.cmake
+Makefile
+test/attitude
+test/cmake_install.cmake
+test/CMakeFiles/
+test/copyto
+test/coverage.info
+test/CTestTestfile.cmake
+test/filter
+test/hatvee
+test/helper
+test/integration
+test/inverse
+test/Makefile
+test/matrixAssignment
+test/matrixMult
+test/matrixScalarMult
+test/out/
+test/pseudoinverse
+test/setIdentity
+test/slice
+test/squareMatrix
+test/transpose
+test/vector
+test/vector2
+test/vector3
+test/vectorAssignment
+Testing/