Move CSFML source files to CSFML/ directory

This helps make it easier to distinguish SFML files from CSFML files.
This is especially important for CSFML private headers which are
often C++ code with .hpp file extensions. This change means SFML and
CSFML can use headers with the same name without conflict.

examples/example.c

@@ -1,5 +1,5 @@
-#include <SFML/Audio.h>
-#include <SFML/Graphics.h>
+#include <CSFML/Audio.h>
+#include <CSFML/Graphics.h>
 
 #include <stdlib.h>