Represents an added neuron. When a neuron is added to a neural network in NEAT an existing connection between two neurons is discarded and replaced with the new neuron and two new connections, one connection between the source neuron and the new neuron and another from the new neuron to the target neuron. This struct represents those three IDs. This struct exists to represent newly added structure in a history buffer of added structures. This allows us to re-use IDs where a mutation recreates a structure that has previously occurred through previous mutations on other genomes.
