Release B-tree version 2.0.0-alpha.25.
Release B-tree version 2.0.0-alpha.25.

 * Return a structure form `nullCursor.indexOf()`. Closes #625.
 * Return a struction from `indexOf` on deleted page. Closes #624.
 * Add bogus `items` to `nullCursor` page. Closes #623.
 * Add `compare` and `extract` to `Racer`. Closes #622.

Closes #626.

bigeasy/strata,bigeasy/strata