Write unittests for ...

[Robbepop]

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

Missing unittests are:

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