Add missing actions to main export

[davidkpiano]

The log, pure, choose, and stop actions were added to the main export:

import { log, pure, choose, stop } from 'xstate';

[changeset-bot]

🦋 Changeset detected

Latest commit: 0b9e4aa

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
xstate	Minor

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Sandbox	Source
XState Example Template	Configuration
XState React Template	Configuration

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[mellson]

It looks fine to me. And since it's not breaking any old APIs I guess the change should be harmless.