Added window/fullscreen and screen buffer

Using a sf::RenderTexture to render the entire screen and then rendering
that texture to the window. Also added flag for fullscreen and it can be
toggled with F11.
Cleaned up #imports for hikari files
Reordered imports
Converted #include directives from <> to ""

For all hikari files I changed all #include<hikari/...> directives to
#include "hikari/..." so the library path won't be searched.