Storage errors cause node to exit

[FauxFaux]

If the storage system throws an error, the exception unwinds back to here:

automerge-repo/packages/automerge-repo/src/Repo.ts

Lines 34 to 38 in d3616cd

	this.on("document", async ({ handle, isNew }) => {
	if (storageSubsystem) {
	// Save when the document changes
	handle.on("heads-changed", async ({ handle, doc }) => {
	await storageSubsystem.saveDoc(handle.documentId, doc)

It's not valid to return a rejected promise from this event handler, as nothing handles that rejected promise. The default unhandledRejection handler is to exit with status 1, so node exits.

I would rather that node didn't exit when there was an error, and some kind of error handler was called, so I can handle or retry said error.