Fix newline at end of file, add comments

Fix "No newline at end of file" warning. The newline was removed
by commit 47f28a2a78, probably unintentionally.

Add missing comments to #endif statements for clarity and consistency.

src/nanosvg.h

@@ -3005,6 +3005,6 @@ void nsvgDelete(NSVGimage* image)
 	free(image);
 }
 
-#endif
+#endif // NANOSVG_IMPLEMENTATION
 
-#endif // NANOSVG_H
+#endif // NANOSVG_H

src/nanosvgrast.h

@@ -1453,6 +1453,6 @@ void nsvgRasterize(NSVGrasterizer* r,
 	r->stride = 0;
 }
 
-#endif
+#endif // NANOSVGRAST_IMPLEMENTATION
 
-#endif // NANOSVGRAST_H
+#endif // NANOSVGRAST_H