Lots of changes. Main addition: a camera class.

Created a simple camera class, added it to the
test application and made it possible to fly
around whith WASD and mouse (left button pressed).

Added Matrix3 rotations around X-, Y- and Z-axes.
Fixed Matrix3 rotation from axis angle used angle
as radians.

Added SafeNormalize and SafeNormalized methods for
Vector2 and Vector3.