[Signalr-Cpp]Please make constructor of `hub_connection` `public`

[albyho]

We need to create a instance of hub_connection as a filed in a class.

[BrennanConroy]

What's wrong with using the hub_connection_builder? Using the builder is how all implementations of the signalr clients create a connection.

[albyho]

What's wrong with using the hub_connection_builder? Using the builder is how all implementations of the signalr clients create a connection.

hub_connection_builder creates
hub_connection instance in stack and it’s not copyable.

[BrennanConroy]

hub_connection does have a move constructor, so you can move it into a class for storage currently.

We are experimenting with returning a shared_ptr<hub_connection> in aspnet/SignalR-Client-Cpp#36 and that's probably the direction we'll continue on.