add norm and pooling & fix bugs in operators (#249)

add norm and pooling & fix bugs in operators

Author: chaoming0625

brainpy/dyn/layers/__init__.py

@@ -6,3 +6,5 @@
 from .reservoir import *
 from .rnncells import *
 from .conv import *
+from .normalization import *
+from .pooling import *