first draft of SymPyCCode op

```Python
class SymPyCCode(ScalarOp):
    """ An Operator that wraps SymPy's C code generation

    >>> from sympy.abc import x, y  # SymPy Variables
    >>> from theano.scalar.basic_sympy import SymPyCCode
    >>> op = SymPyCCode([x, y], x + y)

    >>> from theano.scalar.basic import floats
    >>> xt, yt = floats('xy') # Theano variables
    >>> zt = op(xt, yt)

    >>> import theano
    >>> f = theano.function([xt, yt], zt)
    >>> f(1.0, 2.0)
    3.0
    """
```