Initial version of C lighting code

Needs *lots* of performance work

src/overviewer.h

@@ -33,8 +33,10 @@ Imaging imaging_python_to_c(PyObject *obj);
 PyObject *alpha_over(PyObject *dest, PyObject *src, PyObject *mask, int dx,
                      int dy, int xsize, int ysize);
 PyObject *alpha_over_wrap(PyObject *self, PyObject *args);
+PyObject *brightness(PyObject *img, double factor);
 
 /* in iterate.c */
 PyObject *chunk_render(PyObject *self, PyObject *args);
+PyObject *chunk_render_lighting(PyObject *self, PyObject *args);
 
 #endif /* __OVERVIEWER_H_INCLUDED__ */