feat: better chip structure

src/chip8_neo.rs

 pub const DISPLAY_WIDTH: usize = 64;
 pub const DISPLAY_HEIGHT: usize = 32;
 pub const RAM_SIZE: usize = 4096;
+pub const STACK_SIZE: usize = 16;
+pub const REGISTERS_SIZE: usize = 16;
 
 pub struct Chip8Neo {
     ram: [u8; RAM_SIZE],
     vram: [u8; DISPLAY_WIDTH * DISPLAY_HEIGHT],
+    stack: [u16; STACK_SIZE],
+    registers: [u8; REGISTERS_SIZE],
+    pc: u16,
+    i: u16,
+    sp: u8,
+    dt: u8,
+    st: u8,
 }