Wind down the old documentation pages

[MrPowers]

The old documentation still exists, see here: https://delta-io.github.io/delta-rs/python/

Here are the next steps:

• Step 1: redirect the old URLs to the new URLs
• Step 2: delete the old pages

It shouldn't be too much work, I think these are the only URLs:

• https://delta-io.github.io/delta-rs/python/
• https://delta-io.github.io/delta-rs/python/installation.html
• https://delta-io.github.io/delta-rs/python/usage.html
• https://delta-io.github.io/delta-rs/python/api_reference.html

[ion-elgreco]

@MrPowers you reckon you could do this still?