Resolves #154 - Now :VECTOR suffix will work on all types of Direction.

The Direction class maintained all of the following members:
euler
rotation
vector

When constructing a Direction from a vector, it would calculate the euler and rotation from the vector, but it didn't reciprocate and do the reverse when constructing a Direction from a Euler or a Rotation.  Now it does, and this means expressions like SHIP:FACING:VECTOR will now work correctly.