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/tick.rs

@@ -1,9 +1,8 @@
 use crate::vm::{error::*, flags::Flags, inst::*, reg::*, vm::*, visit::*, mem::MemCursor};
-use std::io::stdin;
 
 impl Vm {
     pub fn tick(&mut self) -> Result<()> {
-        let next_ip = visit_inst(self)?;
+        let next_ip = self.visit_inst()?;
         self.set_reg(IP, next_ip);
         Ok(())
     }
@@ -23,7 +22,7 @@ impl Vm {
     }
 }
 
-impl InstAcceptor for Vm {
+impl VisitInst for Vm {
     type Out = Addr;
 
     fn cursor(&self) -> MemCursor {