Servicex

Add the `url` property to `StreamInfoFile` - this has the added benefit of making the `url` property consistent between streaming from a `minio` source and a locally copied file.

pyarrow` 3.0 runs just fine with this current code, allowing it in the setup (v1.0 and v2.0 also works).

Improvements:

- Streaming interface to allow the calling application to get at the data as ServiceX finished each unit, rather than waiting until the full request is finished. Caching is integrated into this feature. URLS from ServiceX can also be used.
- Works only with modern versions of awkward (> 1.0) and uproot (> 4.0)
- Default cache location is now `/tmp/servicex_{username}` rather than just `/tmp/servicex`

Fixes:
- Minor documentation improvements
- Cache miss will trigger a transformation of the data rather than an exception
- The wording of some exceptions was improved

Thanks to everyone that contributed to this release!

Penultimate beta - for simple testing.

- Streaming interface
- Using awkward and uproot, the modern versions (no more uproot4 or awkward1 references!).

Fix a minio adaptor bug that somehow crept in.

Now includes the streaming interface as well.