Add mechanism for Business requirements gathering and checks

[MarcinCelej]

Sample:

Business.When(transactionType == TransactionType.OnlinePayment)
        .And(onlinePaymentLimit != null)
        .Requires(paymentAmount <= onlinePaymentLimit)
        .Throws($"Online Payment Amount ({paymentAmount}) exceeds the Online Payment Limit ({onlinePaymentLimit})");

[cezarypiatek]

I can imagine that mixing this API with CallerArgumentExpressionAttribute could allow for generating human-readable documentation based on the code.

[MarcinCelej]

Yep. It is the idea. To allow genaration of markdown documentaion of business requirements.

[MarcinCelej]

@cezarypiatek I've started documenting the Business class - i'm also introducing my new concept test-2-code: https://github.com/synergy-software/synergy.framework/tree/master/Contracts/Synergy.Contracts.Test/Requirements
Please, check that and say what you think. There is BusinessDoecumentation class that is a unit test using Approvals and genereating a markdown file. So it do both: testing with samples and generating docs. It's not refactored to be clean yet.

The power of this approach is that when I change anything (refactor) sample code will be automatically changed and markdown documentation must be regenerated - using Approvals mechanism.

Moreover: the documentation is created with the code (docs-as-code) and can be reviewed with it.

[cezarypiatek]

Sure, I will review it this week.