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