prophet 0.0.4

A neural network implementation with a focus on cache-efficiency and sequential performance.
Documentation
TODO-LIST
=========

This is the list of spontaneous things that are planned for the next update:

 - improve comments of ActivationFn constructors of supported activation functions.
 - improve error handling and implement prophet::Error struct and prophet::ErrorType enum.
 - rewrite NeuralNetwork so that you cannot let it predict data before it hasn't learned anything.
 - convolutional neural network implementation
 - implement neural net generically for ```num::Float``` types
 - parallel implementation for large layers
 - implement serialization and deserialization for neural network instances