Make a disassembly GUI.

[maximilien-noal]

Main features:

• Like the DOSBox debugger, really. More usable / user friendly, thanks to ImGUI.

Future disasm features planned :

• extend the disassembler to also return the argument memory adresses and values, and things like "branch (not) taken" on conditional jumps. A lot of this is inspired by OllyDbg.
• MAME's disassembler also has attributes like STEP_OVER, STEP_INTO on opcodes, for use by the debugger.

The GUI should of course display all of that.