Rename bang->apply

! syntax item has been referred to as "bang" instead of "apply" in some
places, this is fixed

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

src/vm/machine.rs

@@ -34,7 +34,7 @@ pub struct NativeFrame {
 #[derive(Debug, Clone)]
 pub struct QuoteFrame {
     locals: BTreeMap<Word, Option<Value>>,
-    code: Rc<Vec<Inst>>, // TODO - deduplicate this with some kind of shared pointer
+    code: Rc<Vec<Inst>>,
     pc: usize,
 }