Return array type and set dtype to numba type (fixes issue #245)

This is a tentative fix for issue #245: "local numpy array constructed with np.array was not recognized as numpy array".
- Return type if dtype specified.
- Convert dtype to numba type using ``get_dtype()``.

Note: I am not very fluent with the code-base, so there are likely other places where similar changes are required, but this seems to do the trick.