Add options to propagate()

Decay rate and memory performance can now be passed as parameters to propagate(), as an option object:

cns.propagate({decay: 60, memoryPerf: 0});

Default value: {decay: 40, memoryPerf: 100})

Decay rate is how much each activation value is decayed during each propagation.

Memory performance influences how the activation value diminish, according to the number of activation propagatoins (called age) a node has been not zero.