This doesn't fix anything yet but maybe running non-ancient versions will make
it easier to fix something.

Update servant-prometheus library to get conforming metric names

Add note about getting the PrivateStorageio environment first

Got it to compile!
This could be chinese for all I know.

The author of the library used says the tests currently fail.
This might be a problem with how Nix handles things.

Also, client-side quantile computation is not available
anymore.  We'll just user server-computed histograms instead.

Add tests for CORS behavior

And now they all pass so everything works fine, great???

Fix a currency and price

Pull the Currency parsing into the JSON parser

Fix the charge/voucher metadata mismatch error handling case

no point really except maybe it is easier to read?  I was trying to remove a
level of nesting but I failed.

We can't control whether Stripe puts the voucher we supply in its metadata.
We can control whether we put the Stripe ChargeId Stripe supplies in our
database, though.

This lets me add a new charge_id column to the vouchers table.
This lets us associate vouchers with transactions on our side.
This provides redundancy with the association on the stripe side.
With this redundancy we can let metadata mismatches go by
(maybe with logging/alerting)
instead of making them fail the whole process.

Add tests to the Nix packaging

The new stanza is the automatic result.

Do a better job generating sensible error results from the payment endpoint

Stripe CardError is now the only error to receive a "Stripe charge didn't
succeed" response.  Other Stripe errors can now fail in other ways.

This is a better client interface and makes HTTP status codes more accurately
reflect the failure which makes them more usable as a monitorable metric.

Add a metric for signatures issued

Record first successful redemption of any voucher, counter pair

So, let it.  Just demonstrate we at least see the test metric.