Add get_opts and get_ranges

[kylebarron]

• The underlying get_opts returns a GetResult. So ideally it would be nice to return a Python object that wraps this GetResult so that in the future we could potentially stream a result into a Python AsyncIterator. However I don't think that would ever be possible because its bytes and into_stream consume self. And you can't have a Python method that consumes self.

  So I think the best approach is to currently return bytes and potentially in the future have a separate get_opts_stream method that returns an async iterator.

I had tried with

#[pyclass(name = "GetResult")]#[derive(Debug)]pubstructPyGetResult{rt:Arc<Runtime>,result:Arc<Mutex<GetResult>>,}#[pymethods]implPyGetResult{pubfnbytes(&self) -> PyResult<Cow<[u8]>>{let lock = self.rt.block_on(self.result.lock());let obj = self.rt.block_on(lock.bytes()).map_err(ObjectStoreError::from)?;Ok(Cow::Owned(obj.to_vec()))}pubfnbytes_async<'a>(&'aself,py:Python<'a>) -> PyResult<&PyAny>{
pyo3_asyncio::tokio::future_into_py(py,asyncmove{let obj = self.result.lock().await.bytes().await.map_err(ObjectStoreError::from)?;Ok(Cow::<[u8]>::Owned(obj.to_vec()))})}}

This is implemented on top of #6, and is expected to be reviewed after that.

[kylebarron]

Closing because I implemented this in https://github.com/developmentseed/object-store-rs