schema versioning

[ChrisRx]

There should be a way to version defined schema. This will be important to allow for writing automated migration scripts. This could be something added to the primary key of the struct:

type MyStruct struct {
    ID int `e2db:"id,v=1"`
}

where implicitly it is schema version 0, or it could be implicit to the types themselves based upon a deterministic hash of the fields. In either case the key structure will have to change to allow for the schema version to be inserted into the key (probably just after the table name).