Re: Cube extension kNN support

Since we change the interface of extension we have to change it version and create a migration script.

E.g. you have to rename cube--1.0.sql to cube--1.1.sql and create cube--1.0--1.1.sql to migrate the old version.

For backward compatibility it would be better to keep the old name of cube_distance so that extension with old definition could work with new binary.

Alexander Korotkov.