Introduce an event for when transaction fees are paid (#702)

* Introduce an event for when transaction fees are paid

* Fix

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

polkadot/runtime/src/impls.rs

@@ -20,7 +20,7 @@ use primitives::Balance;
 use sp_runtime::traits::{Convert, Saturating};
 use sp_runtime::{Fixed64, Perbill};
 use frame_support::weights::Weight;
-use frame_support::traits::{OnUnbalanced, Currency, Get};
+use frame_support::traits::{OnUnbalanced, Imbalance, Currency, Get};
 use crate::{Balances, System, Authorship, MaximumBlockWeight, NegativeImbalance};
 
 /// Logic for the author to get a portion of fees.
@@ -28,7 +28,10 @@ pub struct ToAuthor;
 
 impl OnUnbalanced<NegativeImbalance> for ToAuthor {
 	fn on_nonzero_unbalanced(amount: NegativeImbalance) {
-		Balances::resolve_creating(&Authorship::author(), amount);
+		let numeric_amount = amount.peek();
+		let author = Authorship::author();
+		Balances::resolve_creating(&author, amount);
+		System::deposit_event(balances::RawEvent::Deposit(author, numeric_amount));
 	}
 }