add data and dictionary validation

[aspina7]

add a chunk that uses {pointblank} or {assertr} or {validate}to check data validation rules (can set up to use dictionary validation rules directly) and then check if it fits with standard data dictionaries (which leads nicely to R4EPI/epidict#14) and could then also lead on to a chunk linking to either datadict or labelled (or potentially a wrapper around labelled) for sharing clean datasets