Allow creating empty folders

So far it was not possible to create an empty folder that was then was
later filled up with commands (or folders).
Because of that the structure of input.conf had to be based around
the menu.
By creating empty folders with the `ignore` command, that requirement
has been loosened a bit.
Trimming whitespace from `command` was necessary to check for "ignore".

README.md

@@ -253,6 +253,9 @@ If multiple menu items with the same command are defined, **uosc** will concaten
 
 Menu items are displayed in the order they are defined in `input.conf` file.
 
+The command `ignore` does not result in a menu item, however all the folders leading up to it will still be created.
+This allows more flexible structuring of the `input.conf` file.
+
 #### Examples
 
 Adds a menu item to load subtitles:
@@ -274,6 +277,12 @@ esc  quit  #! Quit
 q    quit  #!
 ```
 
+Define a folder without defining any of its contents:
+
+```
+#  ignore  #! Folder title >
+```
+
 Suggested minimal context menu setup to start with:
 
 ```

uosc.lua

@@ -2837,9 +2837,9 @@ state.context_menu_items = (function()
 	local submenus_by_id = {}
 
 	for line in io.lines(input_conf_path) do
-		local key, command, title = string.match(line, '%s*([%S]+)%s+(.*)%s#!%s*(.-)%s*$')
+		local key, command, title = string.match(line, '%s*([%S]+)%s+(.-)%s+#!%s*(.-)%s*$')
 		if not key then
-			key, command, title = string.match(line, '%s*([%S]+)%s+(.*)%s#menu:%s*(.-)%s*$')
+			key, command, title = string.match(line, '%s*([%S]+)%s+(.-)%s+#menu:%s*(.-)%s*$')
 		end
 		if key then
 			local is_dummy = key:sub(1, 1) == '#'
@@ -2859,6 +2859,7 @@ state.context_menu_items = (function()
 
 					target_menu = submenus_by_id[submenu_id]
 				else
+					if command == 'ignore' then break end
 					-- If command is already in menu, just append the key to it
 					if target_menu.items_by_command[command] then
 						local hint = target_menu.items_by_command[command].hint