spanner: support embedded structs

Hello.

With the spanner package, it is currently impossible to write and retrieve structs that embedded other structs.

For example:

type (
    RecordData struct{
        ID string
        CreatedAt, UpdatedAt time.Time
    }
    User struct{
        RecordData
        FirstName, LastName, Email string
     }
)

Whenever attempting to use the toStruct method of spanner.Row, the spanner package is unable to locate fields from an embedded struct.

The go driver for Mongo DB, here, implemented this feature really well. Can something similar be developed for the spanner package?

[jba]

I believe this is fixed. Anyway, I can no longer reproduce.