change data serialization methods to auto ref in

[tchaloupka]

Also allow data to have disabled copy constructor.

[s-ludwig]

Nice that this works now for all supported compilers, this should definitely work in some way. Unfortunately, requiring getters and toXXX to be const, this is a hard breaking change. Wouldn't just auto ref without the in work, too (letting T be inferred as const)?

[tchaloupka]

Agreed would definitely break something.
I've lessened it just to auto ref and moved type qualifier awareness to serializers to handle as required.
It seems ok, but I'm not so sure all the cases are handled properly as it's a bit magic sometimes :)

[s-ludwig]

Thanks, this looks good now. The only thing I'm still wondering is how the correct isXSerializable traits should look like. I'm thinking about something like this, because the trait should only yield true for const(T) when it actually has a const toX method:

enum isXSerializable(T) = is(typeof(T.init.toX()) : X) && is(T.fromX(X.init) : T);

[tchaloupka]

I've made the change, hopefully in the expected way :) Tests passed ok for me.

[s-ludwig]

Looks good as far as I can tell. Thanks and sorry for losing track of this PR until now.