Composition of clients and servers

[rnett]

Consider a situation where you have two separate servers, but some logic and endpoints are shared. This should be supported by creating the shared components on a Krosstalk object, then including said object in the other ones.

Open questions:

• What is included? Just endpoints? Scopes (almost definitely, but it's more complicated than that)? Serialization? Probably don't want to actually create the included krosstalk objects.
• Include, but under a prefix? This is pretty common for components.

A common enough use case would be for the shared krosstalk to define an Auth scope, that then is implemented by any includers. How to do this? Implies shared scope is an interface, implemented by includers' scopes. But that doesn't work very well if the shared scope is non-abstract. Maybe differentiate between abstract and non-abstract, only allow including abstract? Also could clarify question 1.

This also needs to work across module boundaries

[rnett]

I am also going to need to ensure that all included krosstalks come from the same version of Krosstalk.