refactor to actual modules

src/prolog/codegen.rs

@@ -1,11 +1,14 @@
 use prolog_parser::ast::*;
 
-use prolog::instructions::*;
 use prolog::allocator::*;
 use prolog::arithmetic::*;
+use prolog::clause_types::*;
 use prolog::fixtures::*;
+use prolog::forms::*;
 use prolog::indexing::*;
+use prolog::instructions::*;
 use prolog::iterators::*;
+use prolog::machine::machine_indices::*;
 use prolog::targets::*;
 
 use std::cell::Cell;