Fixed PropData/PropDatum confusion
    * Can't have Reader PropDatum, duh
      Each layer needs its own Datum, and we're in the
      same monad
    * Propogation
        * Changed BackpropResult to RWS PropConfig Updates ([Update],
          PropData)
        * Removed PropDatum and associated lenses
    * Weights, Activator
        * Changed backprop methods to reflect signature change
        * Each method now peels off the appropriate layer from PropData
          when it's done with it
    * Layer, NeuralNet
        * Changed backprop methods to reflect signature change
Added training functions, inverted transformers
    * Propogation
        * Working with RWST over Either proved to be more
          correct than the inverse, so inverted PropResult
          and BackpropResult
    * Weights, Layer
        * Altered prop/backprop functions to reflect
          transformer inversion
    * NeuralNet
        Added predict, train, train1
Added random weight init, conveninece constructors
    * nunavut.cabal
        * updated build-depends and module list
    * Weights
        * Added initWeights
    * NeuralNet
        * Added unsafeAddLayer
        * changed mkFFNet to simpler interface
    * Layer
        * Added initLayer
Factored out error functions to own file
    * Complex enough for it and would like Show instance
    * Changes internal dependency structure, Signal/ErrorSignal
      moved to Nunavut.Signals
    * Updated imports in all other modules to reflect new dependency
      structure
    * Added sumOfSquares error function
Big testing update
    * Arbitrary
        * Finally found a clean(er) way to abstract
          Arbitrary and dimension matching over various
          vector/mtx wrappers
        * Added SizedGen class, various MatchingDims wrappers
    * ActivatorSpec
        * Updated propogation tests to reflect new signatures
        * Added fuzzy equality to codomain tests
    * WeightsSpec
        * Basic testing of propogation dimension matching
    * LayerSpec
        * Same as above