Add basic blocks and implementation of flattening thunks -> basic blocks

* Basic are a more linear way of representing code. Thunks beget basic
  blocks, which beget vectors of instructions.
* Basic blocks are also being flattened into a vector of instructions
  (hopefully, no tests done yet)
* OH yeah locals can be collected too (but currently are not being
  collected in the compiler, that should come soon)

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

src/vm/consts.rs

@@ -1,17 +1,6 @@
 use crate::obj::prelude::*;
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
-pub struct ConstHandle(usize);
-
-impl ConstHandle {
-    pub fn index(&self) -> usize {
-        self.0
-    }
-
-    pub fn new(handle: usize) -> Self {
-        ConstHandle(handle)
-    }
-}
+handle_type!(ConstHandle);
 
 #[derive(Debug, Default)]
 pub struct ConstPool {

src/vm/frame.rs

@@ -1,6 +1,5 @@
 use crate::obj::prelude::*;
 use shredder::{GcSafe, Scan, Scanner};
-use std::collections::BTreeMap;
 
 /// A stack call frame.
 #[derive(Debug, Clone)]
@@ -25,8 +24,6 @@ unsafe impl Scan for FrameKind {
 
 unsafe impl GcSafe for FrameKind {}
 
-pub type Locals = BTreeMap<usize, ObjRef>;
-
 #[derive(Scan, Debug, Clone)]
 pub struct Frame {
     locals: Locals,

src/vm/inst.rs

@@ -25,7 +25,7 @@ pub enum Inst {
     ///
     /// In code, it would look like this:
     ///
-    ///     target.symbol = source
+    /// `target.symbol = source`
     ///
     SetAttr(Sym),
 

src/vm/mod.rs

@@ -81,8 +81,6 @@ impl<'c> Vm<'c> {
     /// Set the next program counter value.
     ///
     /// This may cause the running program to crash. Handle with care.
-    ///
-    /// TODO : consider making this `unsafe`? Is that appropriate in this context?
     pub fn set_pc(&mut self, pc: usize) {
         self.pc = pc;
     }