Update Bill.cs (Add CreateAndSetReference(string) method)

[LEC-Group]

Add new method "CreateAndSetReference".

[manuelbl]

Thanks for your contribution. What would a typical use case be where the new method would be helpful?

In its current form, the PR requires additional work:

• Good documentation is needed
• Test cases are needed
• Throwing untyped exceptions should be avoided
• The handling of white-space and null value should be more similar how other methods do it and it should preferably use the same methods to do it

[LEC-Group]

Yes it's true, the code is not very clean but I find the functionality interesting because it allows to automatically choose the type of reference according to the IBAN and therefore not to worry about the type of reference.

[manuelbl]

Can you be more specific about the use case? What's the greater context of the use case? In what kind of task would it be used? Would the task be executed by a person or in an automated fashion? What would the source of the bill reference be (randomly made up, accounting program etc.)? Would the account number be set before or after the reference and how would conflicts between the type of reference and type of account be resolved?