* feat: fix bug whereby changes made by integration mw were not persisted

This bug meant that this code did not send an event with a userId=bar
to segment.io. This change will result in this code sending an event
with userId=bar to segment.io:

f=function(payload, integration, next) {
	payload.obj.userId = "bar";next(payload);
};
analytics.addIntegrationMiddleware(f);
analytics.identify();

* feat: add addDestinationMiddleware function

WIP

* feat: correct doc

* feat: update addDestinationMiddleware docs

* feat: update dest mw signature to be consistent with source mw

* chore: fix syntax error

* chore: fix failing tests

* chore: fix failing test by enabling integration

* feat: fix multiple invoke events being emitted

* chore: touch HISTORY.md to fix build error

* chore: fix HISTORY.md

* chore: resolve review comments

* chore: bump package version

Co-authored-by: Matthew Ault <matthew.ault@segment.com>