Split up src/obj.rs

* common macros are in their own private module
* functions are in their own obj::function module

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

src/disassemble.rs

@@ -1,4 +1,5 @@
-use crate::obj::{ObjP, UserFunctionInst};
+use crate::obj::function::UserFunctionInst;
+use crate::obj::ObjP;
 use crate::vm::{Chunk, JumpOpArg, Op};
 
 type Row = (String, String, &'static str, String, String);