libdeng2|Asset: Added missing member
libdeng2|ByteRefArray: Clearing/filling the array

A convenient way to zero memory instead of using std::memset.
libdeng2|Math: Degreee/radian conversion
libdeng2|Vector: Added more methods, explicit Euclidean/homogeneous conversion
libdeng2: Cleanup
libdeng2: Added 3x3 and 4x4 matrix templates

Augmented the vectors test to do some matrix math as well.