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/Cargo.lock

@@ -2057,9 +2057,9 @@ dependencies = [
 
 [[package]]
 name = "honggfuzz"
-version = "0.5.47"
+version = "0.5.49"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c3de2c3273ef7735df1c5a72128ca85b1d20105b9aac643cdfd7a6e581311150"
+checksum = "832bac18a82ec7d6c21887daa8616b238fe90d5d5e762d0d4b9372cdaa9e097f"
 dependencies = [
  "arbitrary",
  "lazy_static",