implemented 'tags' pragma

tests/reject/teffects4.nim

@@ -0,0 +1,24 @@
+discard """
+  line: 23
+  errormsg: "type mismatch"
+"""
+
+type
+  TObj = object {.pure, inheritable.}
+  TObjB = object of TObj
+    a, b, c: string
+    fn: proc (): int {.tags: [FReadIO].}
+  
+  EIO2 = ref object of EIO
+
+proc q() {.tags: [FIO].} =
+  nil
+  
+proc raiser(): int =
+  writeln stdout, "arg"
+  if true:
+    q()
+
+var o: TObjB
+o.fn = raiser
+