Move eigen to third party (#282)

* remove useless statement

* Add eigen to third_party dir

* remove reducdant lines

third_party/eigen/unsupported/doc/examples/EulerAngles.cpp

@@ -0,0 +1,49 @@
+#include <iostream>
+#include <unsupported/Eigen/EulerAngles>
+
+using namespace Eigen;
+
+int main() {
+  // A common Euler system by many armies around the world,
+  //  where the first one is the azimuth(the angle from the north -
+  //   the same angle that is show in compass)
+  //  and the second one is elevation(the angle from the horizon)
+  //  and the third one is roll(the angle between the horizontal body
+  //   direction and the plane ground surface)
+  // Keep remembering we're using radian angles here!
+  typedef EulerSystem<-EULER_Z, EULER_Y, EULER_X> MyArmySystem;
+  typedef EulerAngles<double, MyArmySystem> MyArmyAngles;
+
+  MyArmyAngles vehicleAngles(
+      3.14 /*PI*/ /
+          2, /* heading to east, notice that this angle is counter-clockwise */
+      -0.3,  /* going down from a mountain */
+      0.1);  /* slightly rolled to the right */
+
+  // Some Euler angles representation that our plane use.
+  EulerAnglesZYZd planeAngles(0.78474, 0.5271, -0.513794);
+
+  MyArmyAngles planeAnglesInMyArmyAngles(planeAngles);
+
+  std::cout << "vehicle angles(MyArmy):     " << vehicleAngles << std::endl;
+  std::cout << "plane angles(ZYZ):        " << planeAngles << std::endl;
+  std::cout << "plane angles(MyArmy):     " << planeAnglesInMyArmyAngles
+            << std::endl;
+
+  // Now lets rotate the plane a little bit
+  std::cout << "==========================================================\n";
+  std::cout << "rotating plane now!\n";
+  std::cout << "==========================================================\n";
+
+  Quaterniond planeRotated =
+      AngleAxisd(-0.342, Vector3d::UnitY()) * planeAngles;
+
+  planeAngles = planeRotated;
+  planeAnglesInMyArmyAngles = planeRotated;
+
+  std::cout << "new plane angles(ZYZ):     " << planeAngles << std::endl;
+  std::cout << "new plane angles(MyArmy): " << planeAnglesInMyArmyAngles
+            << std::endl;
+
+  return 0;
+}