fix: list MAME's hash, plugins and floppy sounds

The libretro core passes system/mame/{hash,plugins,samples} (retro_init.cpp:111-155). Software lists are required in mamemess, where softlists are on by default. The trees and the 19 floppy samples are collected from libretro/mame at the pin.

bios/Other/mame/plugins/cheat/cheat_json.lua

@@ -0,0 +1,12 @@
+local jsoncheat = {}
+
+function jsoncheat.filename(name)
+	return name .. ".json"
+end
+
+function jsoncheat.conv_cheat(data)
+	local json = require("json")
+	return json.parse(data)
+end
+
+return jsoncheat