Invoice Tags only populate 1st time on collection assignment

[rsafier]

When setting field such as Features and RoutingInfos the tags are generated only on assignment of collection. This pattern is not completely obvious to consumer.
Would be nicer if dynamically built tags only on encode, or provide helper extension methods that abstract that away e.g. Invoice.AddFeatureFlag(x) invoice.AddRouteHint(x)

[nGoline]

This behavior was already a problem to me on the first iteration. I'm changing it to meet the expectations, meaning when you change the Features and/or RoutingInfo the string is re-computed.

[nGoline]

I still think there's room for improvement, like:

• Should we allow for replacing such fields completely (re-assigning the collection)?
• What about other fields?

I welcome any input on this...