release/v3.0.0-preview.4

[andreise]

Taggeds:

• Update Unit dependency to v3.0.2
• Update the test dependencies

Failure:

• Use InvariantCulture instead of Ordinal for FailureMessage when comparing Failure values
• Embrace FailureCode value with quotes in ToString(): "FailureCode": "SomeCode" instead of "FailureCode": SomeCode (to prevent cases like "FailureCode": Some Code with whitespaces, since TFailureCode is a struct, not only a enum)
• Improve ToString() performance: Use CompositeFormat
• Improve the tests