Float.toPrecision/toFixed

Float.toPrecision(int)
int -> string

```
$f = 5.123456;
$f.toPrecision(); //"5.123456"
$f.toPrecision(5); //"5.1235"
$f.toPrecision(2); //"5.1"
$f.toPrecision(1); //"5"
```

Float.toFixed(int)
int -> string

```
$f = 5.123456;
$f.toFixed(); //"5.123456"
$f.toFixed(1); //"5.1"
$f.toFixed(2); //"5.12"
$f.toFixed(3); //"5.123"
$f.toFixed(10); //"5.1234560000"
```
