Finish up branch implementation

* while and unconditional loops are now supported fully
* break and continue keywords for loop control
* List::thunkify() has been broken into its own structure so it can be
  broken out further as necessary

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

src/vm/mod.rs

@@ -267,7 +267,12 @@ impl<'c> Vm<'c> {
                 next_pc = addr;
             }
             Inst::JumpTrue(addr) => {
-                if self.condition {
+                if !self.condition {
+                    next_pc = addr;
+                }
+            }
+            Inst::JumpFalse(addr) => {
+                if !self.condition {
                     next_pc = addr;
                 }
             }