Merge pull request #324 from chaoming0625/master

backward compatibility of `brainpy.dyn` module

Author: chaoming0625

brainpy/dyn.py

@@ -4,7 +4,7 @@
 Deprecated. Use ``brainpy.xxx`` instead.
 """
 
-
+from . import neurons, synouts, synapses, synplast, layers, rates