Transaction Email Send() calls are error-prone

[samritchie]

When calling methods like https://github.com/campaignmonitor/createsend-dotnet/blob/master/createsend-dotnet/Transactional/ClassicEmail.cs#L8 the combination of optional named params, variadic to params, and implicit conversion on EmailAddress makes it very easy to get the call wrong (it will compile, but pass the wrong parameters and throw a misleading error message).

I suggest either removing the params and providing overloads for single & multiple 'to' addresses, and/or making the ClassicEmail class public and allowing client code to pass through an instance to Send().