version 1.0.3: screen auto byte, file devices, and corrections

hello!

these are the changes that this new version of the book contains!

• description and use of the screen auto byte on day 6: this is an advanced feature of the screen device that makes it easier to draw multiple sprites with fewer instructions
• description of the two file devices (there was only one before), with the corresponding adjustment of the datetime device.
• some minor corrections, most importantly regarding the button byte in the controller device: in the previous version we mistakenly swapped the A and B buttons.

make sure you download this new version!

we hope you are having a great time learning about uxn! <3