ENH: Added a default value parameter to the NeuronBiased constructor because...

ENH: Added a default value parameter to the NeuronBiased constructor because of Boost.serialization.

src/Neuron/NeuronBiased.h

@@ -30,7 +30,7 @@ namespace lib4neuro {
          * f(x) = x + b
          * @param[in] b Bias
          */
-        LIB4NEURO_API explicit NeuronBiased( double b );
+        LIB4NEURO_API explicit NeuronBiased( double b = 0 );
 
         /**
          * Evaluates 'x + this->bias' and stores the result into the 'state' property