IO buffer write reader, support bit7 and normal mode, contain error check.

Examples

```rust

let mut data = Data::new();

data.writeto(&"adfadfaf"); let v = data.get::()?; asserteq!(v, "adfadfaf");

// le data.writetole(&34u8); let v = data.getle::()?; asserteq!(v, 34u8);

//bit7
let mut hashmap=HashMap::new(); hashmap.insert(1,"123123".tostring()); hashmap.insert(2,"123123".tostring()); data.write_bit7(&hashmap);

let (,v)=data.getbit7::>()?; assert_eq!(v, hashmap);

```