Description
It does occur to me that system_info as it is doesn't actually contain any actual code, and it could be just a JSON file or whatever else is a cool format. Similarly emulator_info just points to emulator_command_lines, so that could solve #124, by having some other way of linking an emulator to how its command line works.
While it's great to have our own list, and that can stay builtin either way, users also need to be able to add their own stuff, and that also shouldn't be code, so we need a way of reading data files into the list anyway.
The only tricky part is platform-specific metadata and emulator command lines I guess - the former we might just say if you add it yourself you don't get metadata (but having mame_software_lists and dat_names would still be useful), the latter… either user-added emulators are assumed to be compatible with every game thrown at them (other than an extension check), or we have some functionality that's like "this emulator has the same compatibility as Cool Predefined Emulator, use the command line for that", or some stripped down version of that (e.g. for a NES emulator, you can say which mappers it supports).
And configs might be janky I guess but I dunno.