Add (basic, barely working) menu
Select menu entries using mouse or keyboard
Choose menu items using enter or mouse click
Wrap around when highlighting menu with keyboard
Position menu using view and size argument
Add background to menu
Allow for submenus (still don't do anything though)
(WIP) Completely rewrite menu to be more adaptable
Fix positions/view of menu items
Try to replace pointers with references
Fix check for when menu is open
Fix menu entry positions
Add QuitEntry for quitting the game

Also make InputReader non-abstract to allow for default process_event
behavior.
Ignore unused paramter warning for InputReader