The scene now owns its renderer, so there is no need to keep a list
of existing renderers and to call Renderer::Get().

We used to have lol::map::empty() to empty maps, but in std::map
this method is called clear(). It sounds safe to harmonise between
our types and have lol::array::clear() too.

The containers no longer force the user to use the ptrdiff_t type for
size information. For convenience, size() now always returns an int,
and the size_s() method offers a way to handle arrays with more than
2 billion elements. Internally, we still use ptrdiff_t, though.

Since so much code had to be changed, I took the opportunity to get
rid of capitalised accessors for classes that are lowercase.

Implemented Safe-Enum for everyone.
Now the power is in the Safe-Enum for all.

Camera & vector.cpp : Fixed shifted_perspective crash with almost zero FOV.