Add object layout, object parsing, instruction layout

* Object layout and parsing are done in the vm::obj module
* Add MemCursor, a wrapper around the std::io::Cursor type for walking
  through VM memory
* Add vm::tick module for containing the Vm::tick() method
  implementation, since it's pretty big
* Instructions are now variable-sized, and are read lazily,
  one-at-a-time directly from memory.
* Add VM runtime error structure
* Probably some other stuff I forgot

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

src/main.rs

@@ -1,3 +1,5 @@
+#![allow(dead_code)]
+
 mod common;
 //mod syn;
 mod vm;