allow embedded struct pointers to work as regular embedded structs do, fixes #35
factor out the code which converts a nested struct mess into a well ordered list of field reflect.Values so it can be reused in NamedQuery, fixes #24
Simplify some reflection code.
Merge pull request #39 from kisielk/master

Simplify some reflection code.
return the address of non-struct pointer fields rather than the pointers;  fixes problems scanning into pointer fields in structs
simplify sqlx test to use _DSN vars instead of the user/pass stuff and to make it easier to write multi-db tests in isolation of the big TestUsage function
embed a pointer to a DB instead of the DB, avoids a data race caused by copying mutexes, fixes #41
skip introspecting structs which implement driver.Valuer OR sql.Scanner;  fixes #40, as sql.NullString is a Valuer but not a Scanner:w