Added pending spec and comments on how to implement attribute_get/attribute_set.
Added pending spec and comments on how to implement attribute_get/attribute_set.

tillsc/dm-core,joevandyk/dm-core,datamapper/dm-core,cardmagic/dm-core,ar-dm/ardm-core,alloy/dm-core,tpitale/dm-core,engineyard/dm-core