Typesystem global instance churn, again

I don't know if I'm ever going to get this right.

It's a massive pain having to pass around the base "Method" type
everywhere. It really makes a lot more sense to have it already defined
someplace statically available. It makes doing like getting an attribute
or vtable entry a lot more ergonomic. Previously we'd have to pass in
the Method type every time, which was silly. Now we can just let the
MethodInst::instantiate() function query it directly. Like, this is
100000% better.

Also, I got rid of get_attr_lazy in favor of get_vtable_attr. I think
that I want to unify get_attr and get_vtable_attr, but that would
require a GC pointer to the "self" object on every object that you
create. That's a bit iffy.

But for now, things are feeling a little better and all the tests are
passing, so that's good at least.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

src/obj/function.rs

@@ -125,7 +125,7 @@ impl Obj for BuiltinFunctionInst {
         }
     }
 
-    impl_base_obj!();
+    impl_base_obj!(BuiltinFunction);
 }
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -216,7 +216,7 @@ impl Obj for UserFunctionInst {
         }
     }
 
-    impl_base_obj!();
+    impl_base_obj!(UserFunction);
 }
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -249,9 +249,9 @@ impl MethodInst {
         }
     }
 
-    pub fn create(ty: ObjP, self_binding: ObjP, function: ObjP) -> ObjP {
+    pub fn create(self_binding: ObjP, function: ObjP) -> ObjP {
         let ptr = make_ptr(Self::new(self_binding, function));
-        ptr.borrow_mut().instantiate(ty.clone());
+        ptr.borrow_mut().instantiate();
         ptr
     }
 
@@ -294,5 +294,5 @@ impl Obj for MethodInst {
         }
     }
 
-    impl_base_obj!();
+    impl_base_obj!(Method);
 }