Replace Overflow-Prone Operations in Staking with Saturating Arithmetic (#2115)

* Improve a few doc string

* Replace overflow-prone operation with saturating.

* Remove whitespace.

* Update wasm; Bump spec;

* Bump impl again.

* Fix review comments.

substrate/node/runtime/src/lib.rs

@@ -59,7 +59,7 @@ pub const VERSION: RuntimeVersion = RuntimeVersion {
 	impl_name: create_runtime_str!("substrate-node"),
 	authoring_version: 10,
 	spec_version: 44,
-	impl_version: 44,
+	impl_version: 45,
 	apis: RUNTIME_API_VERSIONS,
 };