Changes to the documentation, Theano seems compatible with python 3.3

Multi-gpu support

Clarifies Python 3 in documentation

pip install worked fine on my machine

test function is moved to another function

Make it compatible with python 3

Grad argsort

Fix dnn_conv and dnn_pool docs

"each of" the top and bottom, left and right, etc.

tensor ones and make GpuGer conform.

Also fix the logic in dnn_available() so that we always have an error
message to present.

Finally add the context name that failed in the NoCuDNNRaise error message.