Add setter for link weight range for NEAT populations

* The previous default value of 5.0 seems to come from HyperNEAT
* K. Stanley uses a value of 1.0 in his paper and his code
* Using a large weight range for regular NEAT results in new nodes
  hardly ever being added because doing so causes too great a change
  in the network (since the output link for the new node is set to the
  weight range value)
Merge pull request #187 from JayH5/neat-weight-range

Add setter for link weight range for NEAT populations