Fix delayed subscription missing first message and change topic name

[tony-p]

Fixes issue #51

• For delayed subscriptions (only connect on tick) get the last message
• If topic name changes, actually update subscription
• Also includes Allow subscriber message retention policy to be customised #44

[facontidavide]

I don't understand why by default this should return true. Can you elaborate? When should a user override this?

[tony-p]

That retains current behaviour of the node. Anything else and current default implementation behaviour will change

[facontidavide]

Thanks, but I would not customize the retention policy through inheritance.

Also, it is not very clear what the intent is. What about adding a parameter in the constructor, such as bool latching or change the vistual function to override to bool isLatching() const?

[tony-p]

Thanks, but I would not customize the retention policy through inheritance.

Also, it is not very clear what the intent is. What about adding a parameter in the constructor, such as bool latching or change the virtual function to override to bool isLatching() const?

It is more flexible (some more discussion in #42). For example a colleague wanted to clear it based on a port value, this can easily be added in the overridden definition, although for those particular use cases I think it was better to just define 2 actions

Maybe there are other uses cases basing it on the content of the message itself ... but haven't hit that myself yet

Definitely open to better naming