* initial

* optimize andadd tests

* Update src/exchanges/execute.ts

* Remove unused vars

* Move execute exchange to it's own package

* Update getting started guide

* Remove extras

* Remove extras again

* Update exchanges/execute/src/execute.test.ts

* Update exchanges/execute/src/execute.ts

* Execute exchange: update package.json to align with new conventions & dependency versions.

* Execute exchange: fix failing test.

* Execute exchange: misc code cosmetics from PR review.

* Execute exchange: add empty CHANGELOG.md.

* Execute exchange: fix typo in README.md.

* Execute exchange: allow contextValue to be a function.

* Execute exchange: changes based on PR comments.

* Execute exchange: instead of exposing core's internal method, copy to exchange's package.

* Execute exchange: add test that execute and fetch exchanges both return same data for same inputs.

* Execute exchange: Add teardown support

* Execute exchange: Add to CodeSandbox CI
Co-authored-by: Amy Boyd <amy@amyboyd.co.uk>