Math::mat3 modified

Added Null() method, additional constructor
Bug fixed in cubic equation solving
Math::vec3 modified

Added Null() method, Chop() method
Eigen values and eigen vectors calculation finaly found and added
Additional renderble primitives added (Triangles, TriangleFans and TriangleStrips)
Added unit tests for bounding box construction
Scilab test data cooking added for covariance matrx, eigen values and eigen vectors