Deep refactoring.

1) Kill MatrixXpr class, instead let all class inherit a common EigenBase class
2) Kill MatrixBase/Matrix/Vector classes, instead introduce a single Matrix class,
a MatrixStorage class, and typedefs to emulate vectors
3) Huge code cleanup, remove large preprocessor macros, sloccount drop to ~750
down from 1100.
4) Introduce compile-time-known sizes

src/Core

@@ -26,7 +26,7 @@
 #ifndef EIGEN_CORE_H
 #define EIGEN_CORE_H
 
-#include "internal/Vector.h"
+//#include "internal/Vector.h"
 #include "internal/Matrix.h"
 
 #endif // EIGEN_CORE_H