Add version endpoint to pandoc-cgi

pandoc-cgi/PandocCGI.hs

@@ -44,6 +44,8 @@ type API =
   "convert" :> ReqBody '[JSON] Params :> Post '[PlainText, JSON] Text
   :<|>
   "convert-batch" :> ReqBody '[JSON] [Params] :> Post '[JSON] [Text]
+  :<|>
+  "version" :> Get '[PlainText, JSON] Text
 
 app :: Application
 app = serve api server
@@ -54,6 +56,7 @@ api = Proxy
 server :: Server API
 server = convert
     :<|> mapM convert
+    :<|> pure pandocVersion
  where
   -- We use runPure for the pandoc conversions, which ensures that
   -- they will do no IO.  This makes the server safe to use.  However,