add disassembly & display functions

src/vm.rs

@@ -12,6 +12,20 @@ pub enum VM_Instruction {
     BitwiseNot,
 }
 
+impl VM_Instruction {
+    pub fn param_length(&self) -> usize {
+        match self {
+            VM_Instruction::Jmp |
+            VM_Instruction::Call |
+            VM_Instruction::Branch |
+            VM_Instruction::Lit => {
+                1
+            },
+            _ => 0
+        }
+    }
+}
+
 pub struct VM {
     pub data_stack: Vec< VM_Word >,
     pub call_stack: Vec< VM_Word >,