Implement FixedPoint trait. (#5877)

* Implement Fixed trait.

* Fix tests

* Fix tests

* Fix tests 2

* Address review comment regarding from_i129.

* Remove precision by using log10() as suggested in review.

* Add small comments.

* Use checked versions + panic for ops::*.

* Remove repeated test.

* Uncomment test.

* Remove casts.

* Add more comments.

* Add tests.

* Panic on saturating_div_int

* More tests.

* More docs.

* Saturating renames.

* Fix to_bound doc.

* Move some impl to trait.

* Add range

* Add macro pre.

* More round() tests.

* Delete confusion.

* More impl to trait

* Add doc for fixedpoint op.

* Remove trailing spaces.

* Suggested docs changes.

* More tests and comments for roundings.

* Some quickcheck tests.

* Add missing panic, more test/comments.

* Nits.

* Rename.

* Remove primitives-types import.

* Apply review suggestions

* Fix long lines and add some fuzz.

* fix long line

* Update fuzzer

* Bump impl

* fix warnings

Co-authored-by: Gavin Wood <gavin@parity.io>
Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>

substrate/primitives/arithmetic/src/traits.rs

@@ -21,8 +21,8 @@ use sp_std::{self, convert::{TryFrom, TryInto}};
 use codec::HasCompact;
 pub use integer_sqrt::IntegerSquareRoot;
 pub use num_traits::{
-	Zero, One, Bounded, CheckedAdd, CheckedSub, CheckedMul, CheckedDiv,
-	CheckedShl, CheckedShr, checked_pow
+	Zero, One, Bounded, CheckedAdd, CheckedSub, CheckedMul, CheckedDiv, CheckedNeg,
+	CheckedShl, CheckedShr, checked_pow, Signed
 };
 use sp_std::ops::{
 	Add, Sub, Mul, Div, Rem, AddAssign, SubAssign, MulAssign, DivAssign,