Refactoring propogation
    * Want to work with the idea of propogation a little more
      generically.
    * Propogation.hs
        * removed everything, added Propogate typeclass with
          forward propogation and unsafe (no dim checks) versions.
    * Newtypes.hs
        * Moved all Weights code to Nunavut.Layer.Weights
        * Renamed Activaion to Signal
    * Filter, Layer, Activator, NeuralNet
        * Moved data declaration to *.Internal module, added
          Propogate instances
Monadic propogation
    * Activation state of each layer now recorded in a Writer
    * Unified safe and unsafe return types: just EitherT vs IdentityT

    * Newtypes.hs
        * Moved Signal and ErrorSignal to Propogate.hs
        * Moved pnorm to HasVec, where it should have been
          in the first place. Removed HasNorm.
    * Propogation.hs
        * Changed Propogate class as indicated above
    * Activator, Filter, Weights, Layer, NeuralNet
        * Changed Propogate instance to fit new return type
        * So much neater now
    * nunavut.cabal
        * Fixed typo
        * Added mtl, transformers, either dependencies