Added reference links to loss functions

src/layers/stateless.jl

@@ -59,6 +59,7 @@ end
     Kullback Leibler Divergence(KL Divergence)
 KLDivergence is a measure of how much one probability distribution is different from the other.
 It is always non-negative and zero only when both the distributions are equal everywhere.
+https://en.wikipedia.org/wiki/Kullback%E2%80%93Leibler_divergence
 """
 function kldivergence(ŷ, y)
   entropy = sum(y .* log.(y)) *1 //size(y,2)
@@ -69,6 +70,7 @@ end
 """
     Poisson Loss function
 Poisson loss function is a measure of how the predicted distribution diverges from the expected distribution.
+https://isaacchanghau.github.io/post/loss_functions/
 """
 poisson(ŷ, y) = sum(ŷ .- y .* log.(ŷ)) *1 // size(y,2)