规范模块目录和第三方依赖结构

third_party/eigen3/doc/snippets/MatrixBase_applyOnTheLeft.cpp

@@ -0,0 +1,7 @@
+Matrix3f A = Matrix3f::Random(3,3), B;
+B << 0,1,0,  
+     0,0,1,  
+     1,0,0;
+cout << "At start, A = " << endl << A << endl;
+A.applyOnTheLeft(B); 
+cout << "After applyOnTheLeft, A = " << endl << A << endl;