Add 'self' built-in variable high-lighting

queries/highlights.scm

@@ -7,6 +7,10 @@
 ((type_identifier) @type.builtin
   (#match? @type.builtin "^(int|string|Object)$")
   (#is-not? local))
+
+((identifier) @variable.builtin
+  (#match? @variable.builtin "^self$")
+  (#is-not? local))
 ; }}}
 
 ; Keywords {{{

test/highlight/built-ins.tig

@@ -18,6 +18,8 @@ let
   /*      ^ type.builtin */
 
   type Object = int
+
+  var self := "self"
 in
   let
     var c : int := "This is an int"
@@ -33,6 +35,9 @@ in
   print("shadowing is fun");
   /* <- function.builtin */
 
+  self;
+  /* <- variable */
+
   b := print
   /*   ^ variable */
 end

test/highlight/object-oriented.tig

@@ -14,7 +14,7 @@ let
     method meth() : int = self.a
     /* <- keyword.method */
     /*     ^ method */
-    /*                    ^ variable */
+    /*                    ^ variable.builtin */
   }
 
   var object := new B