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/boot.lua

@@ -0,0 +1,29 @@
+-- license:BSD-3-Clause
+-- copyright-holders:Miodrag Milanovic
+require('lfs')
+
+_G._ = emu.lang_translate
+_G._p = emu.lang_translate
+_G.N_ = function (message) return message end
+_G.N_p = function (context, message) return message end
+_G.emu.plugin = {} -- table to contain plugin interfaces
+-- substitute environment variables in the plugins path from options
+local dirs = manager.options.entries.pluginspath:value()
+
+-- and split the paths apart and make them suitable for package.path
+package.path = ""
+for dir in string.gmatch(dirs, "([^;]+)") do
+	if (package.path ~= "") then
+		package.path = package.path .. ";"
+	end
+	package.path = package.path .. dir .. "/?.lua;" .. dir .. "/?/init.lua"
+end
+
+for _,entry in pairs(manager.plugins) do
+	if (entry.type == "plugin" and entry.start) then
+		emu.print_verbose("Starting plugin " .. entry.name .. "...")
+		plugin = require(entry.name)
+		if plugin.set_folder~=nil then plugin.set_folder(entry.directory) end
+		plugin.startplugin();
+	end
+end