first steps to allow easy functors via macros

tests/fields/timplicitfieldswithpartial.nim

@@ -0,0 +1,19 @@
+discard """
+  out: '''(foo0: 38, other1: string here)
+43'''
+"""
+
+type
+  Base = ref object of RootObj
+  Foo {.partial.} = ref object of Base
+
+proc my(f: Foo) =
+  #var f.next = f
+  let f.foo = 38
+  let f.other = "string here"
+  echo f[]
+  echo f.foo0 + 5
+
+var g: Foo
+new(g)
+my(g)