Add datafusion examples to docs

[matthewmturner]

Description

The description of the main changes of your pull request

Related Issue(s)

closes #515

Documentation

[matthewmturner]

Started putting together the docs, based on test in delta_datafusion.rs. I havent been able to actually get querying delta tables to work locally yet, but wanted to publicize the work in case any comments.

[matthewmturner]

@houqp can delta tables be queried with the datafusion python bindings? i can add something for that as well.

[matthewmturner]

and this might be a silly question, but why does the datafusion feature have the ext suffix but s3 and azure dont?

[matthewmturner]

i looked into this on the python side and it seems that the ExecutionContext is missing the register_table method that is used in rust to query DeltaTables. I'll create an issue there to add that functionality as it would be nice to query from python.

now im going to try querying s3 DeltaTable in rust and adding docs for that then i think this should be good.

[houqp]

@houqp can delta tables be queried with the datafusion python bindings? i can add something for that as well.

Probably not yet because I don't think we support taking a list of file paths yet in the current table provider implementation :(

and this might be a silly question, but why does the datafusion feature have the ext suffix but s3 and azure dont?

Because the datafusion feature conflicts with the datafusion crate name. But I learned later that we could use optional dependencies as features directly. I haven't tested it myself, if this works, it would be better to use datafusion as the feature name going forward in our docs.

[matthewmturner]

Probably not yet because I don't think we support taking a list of file paths yet in the current table provider implementation :(

@houqp can you expand on that? I thought since you can query with datafusion in Rust it was just a matter of exposing that via Python with something like a register_table on context.

[matthewmturner]

@houqp ready for review

[houqp]

Thank you @matthewmturner !