This function is called by fprintf_network to write a layer part
of a network file, i.e. the part between LAYERBEGIN and LAYEREND, for each
layer in net. See NET-IO-format for the layout of this part.
NOTE
Since layer- and map-information is only stored for shared weights
neural networks (having the NET.NetFlag field set to SHAREDNET)
this function is only called when the NetFlag field has that value.