Add support for Dhall lang (#532)

README.md

@@ -306,6 +306,7 @@ Css
 D
 Dart
 DeviceTree
+Dhall
 Dockerfile
 DotNetResource
 DreamMaker

languages.json

@@ -270,6 +270,13 @@
       "quotes": [["\\\"", "\\\""]],
       "extensions": ["dts", "dtsi"]
     },
+    "Dhall":{
+      "nested": true,
+      "line_comment": ["--"],
+      "multi_line_comments": [["{-", "-}"]],
+      "quotes": [["\\\"", "\\\""], ["''", "''"]],
+      "extensions": ["dhall"]
+    },
     "DreamMaker": {
       "name": "Dream Maker",
       "line_comment": ["//"],

tests/data/dhall.dhall

@@ -0,0 +1,16 @@
+-- 16 lines 9 code 5 comments 2 blanks
+{- A comment within the interior of a multi-line literal counts as part of the
+   literal
+-}
+
+''
+-- Hello
+{- world -}
+''
+{ some = "thing"
+
+, keys = ["can"
+, "have",
+-- wait for it
+"lists"]
+}