Non-primary key Serial property

[frconil]

Similar to #48 (it was closed in 2011 so didn't dare reopening it)

Is it possible to define a property that has auto-increment/serial/etc without actually being a primary key?
The original ticket mentioned that an object would replace Serial at some point but I couldn't find it in the documentation.

[tpitale]

The funny thing is the mention of dm-types UUID in #48, which I think is broken in dm-types.

[tpitale]

I think this feature still makes sense.