implement `.close()` method to help `jsonApi.close()` clean up

[jokeyrhyme]

This may depend on holidayextras/jsonapi-server#221

I can submit the PRs for this work, I just want to make sure it's not an obviously bad idea first. :)

[jokeyrhyme]

This is related to a FaaS use case (holidayextras/jsonapi-server#219)

[theninj4]

If you've already worked through the changes, we'll gladly take a PR :) I've just opened a new PR to bump our dependencies (the test suite is inherited from jsonapi-server to be sure we've covered every edge case) and get that badges on the repo green.

[jokeyrhyme]

I noticed this project runs all the tests from the server project, after rewiring the storage handler. Pretty neat.

I'll take a look at my feature request over the next few weeks, perhaps. :)