Add some base VM implementations

Some instructions are currently implemented. Others are not. This is
mostly just a checkpoint so I can implement lexical name definitions.

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

src/compile/thunk.rs

@@ -206,6 +206,12 @@ impl Visit for CompileBody<'_, '_> {
     fn visit_atom(&mut self, atom: &Atom) -> Self::Out {
         let thunk = match atom {
             Atom::Ident(ident) => {
+                // TODO : set up lexical name stack
+                //  - think about how lexical names in function defs need to be captured, so no
+                //   references get prematurely GC'd
+                //  - Python uses LOAD_CLOSURE and CREATE_FUNCTION ops, but is this necessary if we
+                //    know the names being closed over at runtime? Hm.
+
                 // get local
                 Inst::PushLocal(global_sym(ident.to_string())).into()
             }