Slightly better error messages (#150)

* Slightly better errors

Instead of "Unexpected token" we now print
"Unexpected token, expected <type.label>"

test/fixtures/experimental/function-sent/inside-function/options.json

@@ -1,3 +1,3 @@
 {
-  "throws": "Unexpected token (2:17)"
+  "throws": "Unexpected token, expected ( (2:17)"
 }