Tweak coordinatePrism'

[tonymorris]

<edwardk> you can also tweak coordinatePrism to take one pair of constraints easily, by Store or Context as what you decode with
<edwardk> coordinatePrism' :: (AsLatitude (->) Store lat, AsLongitude (->) Store lon) => Prism' (lat, lon) Coordinate
<edwardk> er, (Store lat) and (Store lon)
<edwardk> (or Context lat lat / Context lon lon