Write unittests for ...

[Robbepop]

Write remaining unittests for the new (and old) components of this library.

Missing unittests are:

• utils.rs:
  • LearnRate
  • LearnMomentum
• nn.rs:
  • NeuralNet
• topology_v4.rs:
  • FullyConnectedLayer
  • ActivationLayer
  • AnyLayer
  • LayerSize
  • Topology
  • InitializingTopology
• layer:
  • ActivationLayer
  • FullyConnectedLayer
  • ContainerLayer
  • AnyLayer
    • utils module:
      • buffer_base module
      • matrix_base module
• trainer:
  • utils module:
    • MeanSquaredError
  • mentor module:
    • Context
    • Mentor
    • InitializingMentor