Improved Performance and more

After finally being able to test Astrosweeper on a real Playdate, I was able to make some improvements to the game:

• Performance while moving around is much smoother now
• The first tile you open is now always a blank tile, so you never immediately die
• Double-tapping A on an open tile now opens all adjacent tiles that aren't flagged. This makes playing a lot quicker -- you just need to make sure you got your flags right!