Rethinking the default class hierarchy: Milestone 1, Week 1

[rikki cattermole]

I've stopped using shared entirely, it has only one meaning now for me 
and that is: use atomics.

Having it infiltrate everywhere isn't helpful, in fact half the time I 
spent is on fixing casting to and from shared.

This is after trying to implement lock-free concurrent data structures 
in D for like 6 months, so my opinion is slightly tainted with shared 
and atomics in general.