## API Updates
 * `Event::PaymentFailed` now uses an `Option` for its payment hash, which will
   be `None` if the invoice hasn't been received yet for a BOLT12 payment
   (#3192).
 * `Event::PaymentFailed` is now generated instead `Event::InvoiceRequestFailed`,
   which has been removed. When deserialized the latter will be converted to the
   former with `None` for the payment hash (#3192).

## Backwards Compatibility
 * Any `Event::PaymentFailed` generated without a payment hash will deserialize
   with `PaymentHash([0; 32])` when downgrading. This can be treated like an
   `Event::InvoiceRequestFailed` (#3192).
 * An `Event::PaymentFailed` generated with one of the following
   `PaymentFailureReason`s will deserialize with the corresponding reason after
   downgrading to a version prior to 0.0.124:
   - `UnknownRequiredFeatures` to `RecipientRejected`,
   - `InvoiceRequestExpired` to `RetriesExhausted`, and
   - `InvoiceRequestRejected` to `RecipientRejected` (#3192).