add neuroplasticity for output neuron

src/Ironpen.jl

@@ -36,8 +36,8 @@ using .interface
     Todo:
         [] using RL to control learning signal
         [] consider using Dates.now() instead of timestamp because time_stamp may overflow
-        [] training should include adjusting α, neuron membrane potential decay factor
-            which defined by neuron.tau_m formular in type.jl
+        [1] training should include adjusting α, neuron membrane potential decay factor
+            which defined by neuron.tau_m formula in type.jl
 
         [DONE] each knowledgeFn should have its own noise generater
         [DONE] where to put pseudo derivative (n.phi)