verify 2.0.0-nullsafety.1

Validations made simple. An extension based validation DSL.

Change log

[1.2.0] - Null safety support

• Renames Validator to ValidatorT and Validator_ to Validator
• Renames Verify.property to Verify.that
• Adds Verify.at which lifts a validator of a subfield to the subject

[1.1.0] - Changelog

• Added example with bloc and freezed.
• Better support for form validation enabling grouped errors by field.
• Add inOrder sequenced composition.
• Fix all definition
• Updated documentation.