* Add a custom typed builder for Emulator
* Unify qemu_init for usermode and systemmode
* Remove env from qemu init args (it is unused in QEMU in practice)
* expose thread hooks to systemmode
* rename qemu_config to config
* Replace ExitHandler by EmulatorDriver
* Reorder generics alphabetically for Qemu{,Fork}Executor
* Moved snapshot manager to Emulator to continue centralizing mains objects in the same structure
* Reimplementation of CommandManager working with enums instead of tables
* Macro has been adapted to do this work automatically
* Moved snapshot stuff to dedicated module
* Removed many Rc<RefCell<...>>, now useless with the removal of vtables
* Builder given by Emulator via `Emulator::builder`. Reduced trait bound overhead
