Implementation of several different types of autoencoders in Theano.

<li>da.py: Denoising Autoencoder implementation</li>
<li>ca.py: Contractive Autoencoder implementation</li>
<li>sa.py: Sparse Autoencoder implementation</li>
<li>autoencoder.py: Base class for other autoencoder types and basic implementation of a linear autoencoder.</li>