* Start setting up user callbacks system
* Implement RSP callbacks
* move RSP callbacks (and related RSP stuff) to its own file
* Move destroy_ui to gfx_callbacks_t and change recomp::start to require rsp_callbacks_t
* error_handling.hpp
* Remove UserCallbacks in favor of threads_callbacks_t
* Add `ultramodern::set_callbacks` and some other cleanups
* Move most RSP stuff to librecomp
* Rename rsp_stuff.hpp to rsp.hpp
* Add rsp.cpp to librecomp cmake file
* review
* Remove `recomp::message_box`
* Fix missing rename
