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/Cargo.toml

@@ -20,12 +20,12 @@ num-traits = { version = "0.2.8", default-features = false }
 sp-std = { version = "2.0.0-dev", default-features = false, path = "../std" }
 serde = { version = "1.0.101", optional = true, features = ["derive"] }
 sp-debug-derive = { version = "2.0.0-dev", default-features = false, path = "../../primitives/debug-derive" }
-primitive-types = { version = "0.7.0", default-features = false }
 
 [dev-dependencies]
 rand = "0.7.2"
 criterion = "0.3"
 serde_json = "1.0"
+primitive-types = "0.7.0"
 
 [features]
 default = ["std"]
@@ -35,7 +35,6 @@ std = [
 	"sp-std/std",
 	"serde",
 	"sp-debug-derive/std",
-	"primitive-types/std",
 ]
 
 [[bench]]