This enables the _stage library and adds stage and ugame modules to the
frozen modules, so that all Stage games should work.
I had to do several hacks:
* Since displayio.release_displays doesn't release the pins, I couldn't
re-initialize the display inside the ugame module. Instead I changed
the default display initialization for the board to match what Stage
expects.
* I wanted to make the MENU key works as K_Z, but when I try to use it
with the keypad module, I get "pin in use" error. So for now only the
A and B buttons are used.
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