Updated reqs to interchange >=2021.0.4

Remove Windows test runner

Relaxed rules around subgraph operations; prevented in-place ops (#925)

* Relaxed rules around subgraph operations; prevented in-place ops

* Fixed to_subgraph methods

Artwork for slides

Updated README and docs index

Connector changes for grolt

Fixes #903 by reintroducing entity-level label/key overrides

Removed www dir

Fixed rst in readme

Docs page for py2neo.export