Structure is

     payto://taler-reserve/$HOSTNAME/$PUBLIC_KEY

where $HOSTNAME is a domain name of an exchange operator
and $PUBLIC_KEY is an Ed25519 public key identifying the
long-term reserve public key of a GNU Taler wallet.

Used in GNU Taler to identify a wallet as the target of a
payment.

The "receiver-name" is typically set to "wallet" as often
the actual name of the owner of the wallet is unknown.

We use
     payto://taler-reserve-http/$HOSTNAME/$PUBLIC_KEY

if the exchange service at $HOSTNAME is only reachable
via HTTP. This is usually only used for testing and
generally not supported in production where HTTPS is
required.
