Add function tags

queries/tags.scm

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+; Functions {{{
+(function_declaration
+  name: (identifier) @name) @definition.function
+(primitive_declaration
+  name: (identifier) @name) @definition.function
+
+(function_call
+  function: (identifier) @name) @reference.call
+; }}}
+
+; vim: sw=2 foldmethod=marker

test/tags/functions.tig

@@ -0,0 +1,12 @@
+let
+  primitive print(s: string)
+  /*        ^ definition.function */
+
+  function func(a: int) : int = (print("Hello World!"); a)
+  /*       ^ definition.function */
+in
+  print("Hello World!\n");
+  /* <- reference.call */
+  func(42)
+  /* <- reference.call */
+end