provide pointer to target for scan of json fields

scan varchar into json.RawMessage when struct tag dbtype is json

update go.mod to github.com/watercraft/sqlx

set scannable to false

don't require struct used for parameters not to implement scannable i…

…nterface

add go.sum and updated go.mod w/ test deps

Merge pull request jmoiron#118 from jmoiron/liaoliaopro-master

tag handling for reflectx

update README to refer to shiny new docs