add global error calculation functions, defaults & utility functions
add some more defaults
add synapse + tests
better neuron + more tests
add input & output synapses
add input & output neurons + tests
add layer & network skeletons
Merge branch 'develop'

* develop:
  add layer & network skeletons
  add input & output neurons + tests
  add input & output synapses
  better neuron + more tests
  add synapse + tests
  add some more defaults
  add global error calculation functions, defaults & utility functions

Conflicts:
	test/itsalive/neuron_test.rb