Don't include "word", "dword" prefixes on immediate jump
Add resolver.

Inspired by Dimitry Stogov's patch on GitHub.  However this callback also includes the ud struct pointer, so that you can get the user-specific data and avoid global variables.  Also I'm only using it for jumps at the moment.

This opens up some problems as insn_buffer can now easily overflow with long symbol names.  Fix for that comes next.
1. New call to set the asm buffer to something else.

2. Make sure mkasm() doesn't overflow its buffer.

3. New callback to react to when mkasm() needs more space.  If this callback is missing or doesn't replace the buffer, truncation occurs.