Adding convenience range validators.

[LucianoPAlmeida]

Just a few convenience options to validate ranges :)

[codecov-io]

Codecov Report

Merging #4 into master will increase coverage by 11.96%.
The diff coverage is 97.91%.

@@             Coverage Diff             @@
##           master       #4       +/-   ##
===========================================
+ Coverage   85.24%   97.21%   +11.96%     
===========================================
  Files          32       32               
  Lines        1159     1077       -82     
  Branches      158        0      -158     
===========================================
+ Hits          988     1047       +59     
+ Misses         31       30        -1     
+ Partials      140        0      -140

Impacted Files	Coverage Δ
Quiver/Validating/Extensions/Validator+Range.swift	100% <100%> (ø)	⬆️
...alidating Tests/QuiverIntegerValidatorsTests.swift	100% <100%> (+26.02%)	⬆️
...Validating/Default Validators/RangeValidator.swift	81.25% <80%> (-5.42%)	⬇️
Quiver/Validating/ValidatorEngine.swift	84.31% <0%> (-6.01%)	⬇️
...Validating/Default Validators/RegexValidator.swift	84.61% <0%> (-4.28%)	⬇️
...ating/Default Validators/ComparatorValidator.swift	84.61% <0%> (-3.96%)	⬇️
...alidating/Default Validators/LengthValidator.swift	86.66% <0%> (-3.34%)	⬇️
Quiver/Validating/Validatable.swift	100% <0%> (ø)	⬆️
...idating/Default Validators/RequiredValidator.swift	100% <0%> (ø)	⬆️
... and 25 more

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[heitorgcosta]

I don't think there's a need for a validator for all ranges when all of the range types conforms to the RangeExpression protocol. You can write only one validator with T: RangeExpression and the value to be used in the range~=value expression can be casted into T.Bound, which is a comparable.

Something like this:
class RangeTypeValidator<T>: Validator where T: RangeExpression
the init should be modified to:
init(range: T) instead of init(range: Range<T>)
and in the validation process:
guard let value = object! as? T.Bound else {}
and the object propertie should be a RangeExpression instead of Range<T>

On the convenience methods in the Validator's extensions, only one method is needed:
`public static func range<T: RangeExpression>(_ range: T, message: String? = nil) -> Validator

With these changes, all tests will probably be still passable, with less code and still working.

If you could try that, I would be appreciate :3

[heitorgcosta]

Nice work ✨