Fully merge backend-src and frontend-src (#654)

* Move shared types to Miso.Html.Types module

* Make frontend Attribute type a superset of backend Attribute type

* Use frontend-src Attribute type for backend as well

* Move frontend-only orphans into Miso.Html.Types

* Drop duplicate backend-src AllowDrop type

* Merge View types into a single type

* Merge ToView classes

* Get rid of intermediate VTree in ToHtml View instance

* Move Html View instance into shared Miso.Html.Types module

* Drop trivial Miso.Html.Internal module from backend-src

* Move VTree and runView into shared Miso.Html.Types module

* Drop trivial Miso.Html.Internal module from frontend-src

* Move Miso.Delegate and Miso.Diff from frontend-src to src

* Merge separate Miso modules into single union

* Get rid of JSADDLE cpp

ghcjs-src/Miso/String.hs

@@ -24,9 +24,7 @@ module Miso.String (
   , ms
   ) where
 
-#if !defined(JSADDLE) || defined(__GHCJS__)
 import           Data.Aeson
-#endif
 import qualified Data.ByteString as B
 import qualified Data.ByteString.Lazy as BL
 import           Data.Char
@@ -42,9 +40,6 @@ import           Prelude hiding (foldr)
 -- | String type swappable based on compiler
 type MisoString = JSString
 
-#if !defined(JSADDLE) || defined(__GHCJS__)
-
-
 -- | `ToJSON` for `MisoString`
 instance ToJSON MisoString where
   toJSON = String . textFromJSString
@@ -54,7 +49,6 @@ instance FromJSON MisoString where
   parseJSON =
     withText "Not a valid string" $ \x ->
       pure (toMisoString x)
-#endif
 
 -- | Convenience class for creating `MisoString` from other string-like types
 class ToMisoString str where