Import classes into module __init__

Author: mkelley

sbpy/surfaces/__init__.py

@@ -0,0 +1,7 @@
+from .surface import Surface
+from .lambertian import LambertianSurface
+from .scattered import (
+    ScatteredLight,
+    ScatteredSunlight,
+    LambertianSurfaceScatteredSunlight,
+)