require Virtus, use for :string data type
use Virtus for :float values
use Virtus for :integer values
remove unused :boolean data type
use Virtus for :location values

- establish superclass location parsing for weather services
use Virtus for :timezone values
use Virtus for :symbol values
use Virtus for :temperature values
use Virtus for :vector values

- refactor code to handle unit conversion on attributes
  that respect units
use Virtus for :pressure values
use Virtus for :distance values
use attribute for type :float
Data::Sun is now a Virtus ValueObject
Merge branch 'virtus'