keybinds 

========================================
in main menu
 * A: ROM menu
 * B: VMU menu
 * Y: credit

 * START + Y + L + R: reset. 


========================================
in ROM menu
 * A: move to the directory 
 * Y: move to the parent directory
 * X + UP/DOWN/LEFT/RIGHT: high speed cursor move
 * analog: adjust cursor wait


========================================
in playing game
 * X: GB B
 * A: GB A
 * Y: GB SELECT
 * START: GB START
 * UP/DOWN/LEFT/RIGHT: same as DC

 * L + R + START: exit game

 * B + R: quick save menu
   items
    - quick state save (clear when exit game)
    - quick state load 

 * Y + R: VMU state save menu
   items
    - VMU state save 
    - VMU state load

 * A + R: option menu
   items
    - adjust screen position