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. 
You're right about these two cases. Here the tests are to make sure the functions run given the inputs. I'm resistant to just doing that by itself, so I added len() as a way of testing something constant - something that was separate from the execution of the function.