修改位操作示例展示效果

[tianq02]

修改示例数据类型为u8。原先的i32长度过长不便01二进制展示；且取反操作会一同反转符号位，或许会造成读者疑惑。
展示输出中使用{:08b}格式化并对齐，应该更加直观。

修改后的运行效果如下

PS D:\pro\rustworks\playground\demo_binop> cargo run
    Finished dev [unoptimized + debuginfo] target(s) in 0.07s
     Running `target\debug\demo_binop.exe`
a value is        00000010
b value is        00000011
(a & b) value is  00000010
(a | b) value is  00000011
(a ^ b) value is  00000001
(!b) value is     11111100
(a << b) value is 00010000
(a >> b) value is 00000000
(a << b) value is 00010000