Add Disassemble, fix bug in position calculation

* Disassemble structure can be used for dumping an object section
* Assembler position calculation was messing up, causing jump addresses
  to be wrong. This is fixed.

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

src/vm/mem.rs

@@ -8,6 +8,7 @@ use std::{
 const R1_MASK: u16 = 0b1111_1100_0000_0000;
 const R2_MASK: u16 = 0b0000_0011_1111_0000;
 
+#[derive(Debug, Clone)]
 pub struct MemCursor<'mem> {
     cursor: Cursor<&'mem [u8]>,
 }