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

The feature will still be accessible from a uniform in the shader, but it
is now disabled by default.

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.

This flag disables GL, GLES, but also Glew and EGL libraries.

Added scissor mode in renderer
Added scissor support in imGui
Mouse scroll sensivity tweak

- removed 0 CR characters
 - removed 7 trailing whitespaces
 - replaced 332 tabs with spaces

- Most recent version is in with index buffer support

Shader replacement code for older shader version is now fixed

This will help us deal with shader name collision. Breaks the Windows
build for the moment, unfortunately.

All these changes will allow us to more easily add Lol Engine as a
submodule of another Git project.

Not all programs support this feature for now, but that’s because they
don’t support the scene framework either, and will need patching. Also
the default postprocess is deliberately exaggerated for now.

There might be issues with lolremez but at first sight it seems to work.