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/fuzzer/Cargo.toml

@@ -15,7 +15,7 @@ targets = ["x86_64-unknown-linux-gnu"]
 
 [dependencies]
 sp-arithmetic = { version = "2.0.0-dev", path = ".." }
-honggfuzz = "0.5"
+honggfuzz = "0.5.49"
 primitive-types = "0.7.0"
 num-bigint = "0.2"
 num-traits = "0.2"
@@ -31,3 +31,7 @@ path = "src/per_thing_rational.rs"
 [[bin]]
 name = "rational128"
 path = "src/rational128.rs"
+
+[[bin]]
+name = "fixed"
+path = "src/fixed.rs"