General update (includes breaking changes)

This PR includes breaking changes:

- e3reader's `isvalid(swipedate)` now returns a tuple `(bool success, dict response)`

Other highlights:

- updates certification (test) and production URLs

- adds url kwarg to PosGateway (defaults to certification URL)

- adds CreditAccountVerify (transactionless verification)

- adds pre-request filter (e.g. for adding properties to elements), half-baked: currently hard-coded to add method="swipe" to TrackData element