Add mem and obj modules, move to nightly

* mem and obj modules are roughly divided between doing memory-specific
  things and object-specific things
* Box::new_uninit() is a nightly feature and it's quite useful, so I'm
  enabling that for now
* Check out src/obj/attrs.rs for possible undefined behavior in the
  Attrs::new() function. I'm sure it'll be just fine.

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

src/main.rs

@@ -1,4 +1,9 @@
+#![allow(dead_code)]
+#![feature(new_uninit)]
+
 mod syn;
+mod obj;
+mod mem;
 
 use std::{
     convert::TryFrom,