refactor election score (#10834)

* refactor election score

* Test for ord

* remove reference

* vec -> slice

* change iter to iter_by_significance

* improve doc

* fix typo

* add explanation about [u128; 3]

* consolidate threshold and epsilon

* random fixes

* rename

* remove Into

* make iter_by_sig private

* remove vec

* Fix tests

substrate/primitives/arithmetic/src/lib.rs

@@ -55,7 +55,7 @@ use traits::{BaseArithmetic, One, SaturatedConversion, Unsigned, Zero};
 /// - `Ordering::Equal` otherwise.
 pub trait ThresholdOrd<T> {
 	/// Compare if `self` is `threshold` greater or less than `other`.
-	fn tcmp(&self, other: &T, epsilon: T) -> Ordering;
+	fn tcmp(&self, other: &T, threshold: T) -> Ordering;
 }
 
 impl<T> ThresholdOrd<T> for T