Integrate MultiVerb into servant package

This commit is Part 1 of the integration, where only the
`servant`Epackage is touched. `Verb` is redefined as an alias for
`MultiVerb1` inEorder to make the transition transparent to users of
`Verb`.

Author: theophile-scrive

servant/servant.cabal

@@ -106,10 +106,12 @@ library
     Servant.API.Sub
     Servant.API.TypeErrors
     Servant.API.TypeLevel
+    Servant.API.TypeLevel.List
     Servant.API.UVerb
     Servant.API.UVerb.Union
     Servant.API.Vault
     Servant.API.Verbs
+    Servant.API.MultiVerb
     Servant.API.WithNamedContext
     Servant.API.WithResource
 
@@ -133,6 +135,7 @@ library
     , containers    >=0.6      && <0.8
     , mtl           ^>=2.2.2   || ^>=2.3.1
     , sop-core      >=0.4.0.0  && <0.6
+    , generics-sop  ^>=0.5.1
     , text          >=1.2.3.0  && <2.2
     , transformers  >=0.5.2.0  && <0.7
 

servant/src/Servant/API/Alternative.hs

@@ -35,7 +35,6 @@ instance (Semigroup a, Semigroup b) => Semigroup (a :<|> b) where
 
 instance (Monoid a, Monoid b) => Monoid (a :<|> b) where
     mempty = mempty :<|> mempty
-    (a :<|> b) `mappend` (a' :<|> b') = (a `mappend` a') :<|> (b `mappend` b')
 
 instance Bifoldable (:<|>) where
     bifoldMap f g ~(a :<|> b) = f a `mappend` g b