parrot_neuron_ps - Neuron that repeats incoming spikes handling  
precise spike times.
The parrot neuron simply emits one spike for every incoming spike.
An important application is to provide identical poisson spike
trains to a group of neurons. The poisson_generator sends a different
spike train to each of its target neurons. By connecting one
poisson_generator to a parrot_neuron and then that parrot_neuron to
a group of neurons, all target neurons will receive the same poisson
spike train.




- Weights on connection to the parrot_neuron are ignored.
- Weights on connections from the parrot_neuron are handled as usual.
- Delays are honored on incoming and outgoing connections.

Only spikes arriving on connections to port 0 will be repeated.
Connections onto port 1 will be accepted, but spikes incoming
through port 1 will be ignored. This allows setting exact pre-
and post-synaptic spike times for STDP protocols by connecting
two parrot neurons spiking at desired times by, e.g., a
stdp_synapse onto port 1 on the post-synaptic parrot neuron.

Please note that this node is capable of sending precise spike times
to target nodes (on-grid spike time plus offset). If this node is
connected to a spike_detector, the property "precise_times" of the
spike_detector has to be set to true in order to record the offsets
in addition to the on-grid spike times.

adapted from parrot_neuron by Kunkel