Big Object naming refactor

* trait Obj -> Object
* Remove *Inst suffix from all object types. ObjInst -> Obj, IntInst ->
  Int, etc
* Type -> Ty, type_inst() -> ty(), type_name() -> ty_name()

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

src/disassemble.rs

@@ -1,4 +1,4 @@
-use crate::obj::function::UserFunctionInst;
+use crate::obj::function::UserFunction;
 use crate::obj::ObjP;
 use crate::vm::{Chunk, JumpOpArg, Op};
 
@@ -151,11 +151,7 @@ pub fn disassemble(chunk: &Chunk, constants: &Vec<ObjP>, globals: &Vec<String>)
     disassemble_chunk(chunk, constants, globals);
 
     for constant in constants {
-        if let Some(fun) = constant
-            .borrow()
-            .as_any()
-            .downcast_ref::<UserFunctionInst>()
-        {
+        if let Some(fun) = constant.borrow().as_any().downcast_ref::<UserFunction>() {
             println!();
             println!(
                 "== {} starting on line {}",