Release notes

• Support validating only specific properties by path.
• Allow specifying a ruleset with SetValidator for complex properties.
• Introduce PropertyValidatorOptions in order to clean up the IPropretyValidator interface.
• Moved the AttributedValidatorFactory into a separate package.
• IStringSource.GetString now takes a context.
• Major cleanup of asynchronous validation workflow.
• Deprecate SetCollectionValidator in favour of RuleForEach().SetValidator
• Remove the pre-7 version of Custom/CustomAsync.
• Removed deprecated localization system.
• Remove deprecated RemoveRule/ReplaceRule/ClearRules methods.