lua add submenu module + cleanup

allows menus + submenus + context menus all with simple tables
menu_t which is a table of strings
func_t which are the corresponding functions to go with those strings

see lua_scripts/submenu_demo.lua

Change-Id: I907b74b4abef0ecbe49f181d0ced6e6d20e94de5

apps/plugins/lua_scripts/submenu_demo.lua

@@ -0,0 +1,93 @@
+--Bilgus 4/2021 Menu with subitems and context demo
+require("printsubmenu")
+
+local scrpath = rb.current_path()
+
+local function get_ctx_menu(parent, sel, menu_t, func_t)
+    local mt = {"Context menu " .. (menu_t[parent] or "ROOT") ..
+            " : " .. menu_t[sel], "Quit", "Action 1", "Action 2"}
+    local ft = {false, function() menu_ctx.quit = true return true end}
+    return mt, ft
+end
+
+local function ITEM_MENU()
+
+    local function flung(i, menu_t, func_t)
+        local parent = get_parent() or 0
+        rb.splash(100, "flung " .. (menu_t[parent] or "?"))
+    end
+
+    local function foo(i, menu_t, func_t)
+        local parent = get_parent() or 0
+        rb.splash(100, "FOO " .. menu_t[parent])
+    end
+
+    local function far(i, menu_t, func_t)
+        local parent = get_parent() or 0
+        rb.splash(100, "far" .. menu_t[parent])
+    end
+
+    return {"Flung", "FOO", "Far"},
+            {flung, foo, far}
+end
+
+local function USERITEMS()
+
+        return {"Item_1", "Item_2", "Item_3"},
+               {create_sub_menu(2, ITEM_MENU()), create_sub_menu(2, ITEM_MENU()),
+                create_sub_menu(2, ITEM_MENU()), function() end}
+end
+
+local function MAIN_MENU()
+
+    local function go_back(i, m, f)
+        local parent = get_parent() or 0
+        if parent > 0 then
+            f[parent](parent, m, f)
+        else
+            menu_ctx.quit = true
+        end
+        menu_ctx.start = parent - 1
+        return true
+    end
+
+    local mt =  {
+        [1] = "lua Menu Demo",
+        [2] = "Items",
+        [3] = "Back",
+        }
+
+    local ft =  {
+        [0]  = go_back, --if user cancels do this function
+        [1]  = false, -- shouldn't happen title occupies this slot
+        [2]  = create_sub_menu(1, USERITEMS()),
+        [3]  = go_back,
+        }
+    return mt, ft, get_ctx_menu
+end
+
+function ShowMain()
+    set_menu(MAIN_MENU())
+end
+
+--ShowMainMenu()
+ShowMain()
+rb.lcd_clear_display()
+rb.lcd_update()
+local lu = collectgarbage("collect")
+local used, allocd, free = rb.mem_stats()
+local lu = collectgarbage("count")
+local fmt = function(t, v) return string.format("%s: %d Kb\n", t, v /1024) end
+
+-- this is how lua recommends to concat strings rather than ..
+local s_t = {}
+s_t[1] = "rockbox:\n"
+s_t[2] = fmt("Used  ", used)
+s_t[3] = fmt("Allocd ", allocd)
+s_t[4] = fmt("Free  ", free)
+s_t[5] = "\nlua:\n"
+s_t[6] = fmt("Used", lu * 1024)
+s_t[7] = "\n\nNote that the rockbox used count is a high watermark"
+rb.splash_scroller(5 * rb.HZ, table.concat(s_t))
+--require("print_lua_func")
+os.exit(1, "Goodbye")