Error if send or receive session expired #299

The bip21 crate already percent encodes query parameters so doing it in UrlExt accidentally doubled the percent encoding. This makes an infallable api.

Default to 24 hour expiration. Throw an error when the relevant request is extracted so that polling can be done until the expiration is thrown. The expiration error type should be accessable so that the caller knows if an error was thrown for expiration or for some other reason.