move resource loading to lava::asset and clean up

CMakeLists.txt

DOCS.md

README.md

liblava/app/app.cpp

liblava/asset.hpp

liblava/asset/mesh_loader.cpp

liblava/asset/mesh_loader.hpp

liblava/asset/scope_image.cpp

liblava/asset/scope_image.hpp

liblava/asset/texture_loader.cpp

liblava/asset/texture_loader.hpp

liblava/lava.hpp

liblava/resource/buffer.hpp

liblava/resource/format.hpp

liblava/resource/image.hpp

liblava/resource/mesh.cpp

liblava/resource/mesh.hpp

liblava/resource/texture.cpp

liblava/resource/texture.hpp