Adds button to the host menu to allow shared lives.
Resolves#37
Buttons are now resizeable. Use gButtonScale.<size> (large, medium, or small).
It could be argued that we don't need the small size. However, it may be beneficial for the future if the menu becomes more complex.
large is the normal default size. Or at least it was the size already being used by sm64ex-coop (0.11111111f)
Note: Buttons for changing menu's should be gButtonScale.large as the menu animation is made for large buttons. To keep consistency it's probably a good idea for buttons that transfer you to a new menu to always be set to large. As such, I didn't feel it necessary to extend this feature to these methods: bhv_menu_button_growing_from_custom and bhv_menu_button_shrinking_to_custom.
Resolves#60
The vanilla main menu is an awful pile of code that is extremely painful
to make additions to. So I've side-stepped the problem by writing an
entiely new menu system without all of vanilla's quirks. I've separated
the custom menu system from the menus I want to make, which allows for
easy additions and a clear separation of responsibilities.
Along with this rewrite comes a host menu, adding the missing
configuration options in-game.
Fixes#29
