Add 'import' high-lighting

queries/highlights.scm

@@ -34,6 +34,10 @@
  "method"
 ] @keyword.method
 
+[
+  "import"
+] @include
+
 [
   "array"
   (break_expression)

test/highlight/imports.tig

@@ -1,3 +1,3 @@
 import "lib.tih"
-/* <- keyword */
+/* <- include */
 /*      ^ string.special.path */

test/highlight/keywords.tig

@@ -10,7 +10,7 @@ let
   /* <- keyword.function */
 
   import "lib.tih"
-  /* <- keyword */
+  /* <- include */
 
   type array_of_int = array of int
   /* <- keyword */