Pgvector

- Added notice when index created with little data
- Fixed dimensions check for some direct function calls
- Fixed installation error with Postgres 12.0-12.2

- Improved performance of cosine distance
- Fixed index scan count

If upgrading with Postgres < 13, see [this note](https://github.com/pgvector/pgvector/blob/v0.4.0/README.md#040).

- Changed text representation for vector elements to match `real`
- Changed storage for vector from `plain` to `extended`
- Increased max dimensions for vector from 1024 to 16000
- Increased max dimensions for index from 1024 to 2000
- Improved accuracy of text parsing for certain inputs
- Added `avg` aggregate for vector
- Added experimental support for Windows
- Dropped support for Postgres 10

- Fixed `invalid memory alloc request size` error

If upgrading from 0.2.7 or 0.3.0, [recreate](https://github.com/pgvector/pgvector/blob/v0.3.1/README.md#031) all `ivfflat` indexes after upgrading to ensure all data is indexed.

- Fixed issue with inserts silently corrupting `ivfflat` indexes (introduced in 0.2.7)
- Fixed segmentation fault with index creation when lists > 6500

- Added support for Postgres 15
- Dropped support for Postgres 9.6