introduce toX methods for DatomicData variants

add toX methods for each DatomicData variant that wraps a basic val type. When the type of data needs to be ascribed, _.to[T] is the correct idiom, but when the variant is already known, _.toX is handy
Merge pull request #4 from pellucidanalytics/topic/toX-methods

introduce toX methods for DatomicData variants