Add object store support

[robtandy]

Basic Object store support

Changes:

• Updated register_parquet, register_listing_table, and added register_csv such that they will automatically register an object store based on the Url of the path provided. Local paths, relative or absolute, are interpreted as a file:// url, using the parse functionality in ListingTableUrl from datafusion.
• Added example/http_csv.py a port of https://github.com/apache/datafusion/blob/45.0.0/datafusion- examples/examples/query-http-csv.rs
• Updated the example in the Readme.md to be a working example using a github hosted csv file.

Object store credentials

In this PR, all object stores are automatically registered - which can be really nice - and the trade off is that we rely on the cloud provider SDKs to gather credentials from their environment, or local files, rather than explicitly providing them.

In a future release we can add more configurability here.

Looks like a few formatting changes snuck in here from editing. I would like to defer sorting out those details until we have commit hooks to ensure proper and consistent file formatting.

[andygrove]

LGTM. Thanks @robtandy.