Added ability to make a DjuiBase keep its aspect ration
Added on_render_pre callback
Added ability to display 32b images
Added DjuiFlowLayout
Added logo
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
