test/transformation: Update documentation
test/transformation: Switch to smart pointers

Use smart pointers for construction tests instead of using `new` directly
inside the Boost test macros.
transformation/orthogonal: Rename parameter `direction` to `lookat`

Rename parameter for consistency between OrthogonalDepthProjection and
OrthogonalProjection. 'direction' even doesn't make much sense (you don't
know if you mean the spanning directions or the normal/lookat direction).
So now call it 'lookat'.
orthogonal_depth_projection: Make constructor parameter `const&`

Construct from `const` reference, not from copy!
orthogonal_depth_projection: Add new constructor for multiple vectors

Add constructor that is also supported in base class. This includes tests
for the new constructor.
transformation: Documentation update

Update documentation comments for OrthogonalProjection and
OrthogonalDepthProjection.