Remove Obj::into_gc() and have Obj ctors return a Gc instead

Since we're nightly and using coerce_unsized, we can just coerce a
Gc<T: Obj> into a Gc<dyn Obj> for free.

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

src/obj/quote.rs

@@ -2,7 +2,7 @@ use crate::obj::{Obj, VTable};
 use crate::syn::ast::SpStmt;
 use crate::vm::{error::*, machine::Machine};
 use crate::{scope::Scope, syn::span::Span, vm::inst::SpInst};
-use gc::{unsafe_empty_trace, Finalize, Trace};
+use gc::{unsafe_empty_trace, Finalize, Gc, Trace};
 use std::fmt::Debug;
 use std::rc::Rc;
 
@@ -27,11 +27,11 @@ pub struct QuoteObj {
 }
 
 impl QuoteObj {
-    pub fn new(value: Quote) -> Self {
-        QuoteObj {
+    pub fn new(value: Quote) -> Gc<Self> {
+        Gc::new(QuoteObj {
             value,
             vtable: vtable! {},
-        }
+        })
     }
 
     #[allow(dead_code)]