Theano computation output

This transforms SymPy expressions into Theano computations.  Theano can then be used to generate relatively high performance code.  Perhaps this is an alternative to lambdify?  Theano can use numpy or CUDA under the hood.

```
In [1]: expr = x**y + 1
In [2]: from sympy.printing.theanocode import theano_code
In [3]: output = theano_code(expr)
In [4]: inputs = map(theano_code, (x, y))

In [5]: from theano import function
In [6]: f = function(inputs, output)
In [7]: f(2, 3)
Out[7]: 9.0
```