Test compute numpy

This is almost ready for merging. I have one problem though, with the function on line 49:

```
@dispatch(BinOp, base, np.ndarray)
def compute_up(t, lhs, rhs, **kwargs):
    return t.op(lhs, rhs)
```

Had a lot of trouble figuring out how to call this function, figuring out what it wanted for inputs. Any feedback on this would be appreciated. 
I've been trying to stay away from using `api` code in `compute`

To me there is a general ordering of `expr-compute-api`.  I try not to use code from the later more user facing modules in the earlier, more core technology ones.