Add fractional class

Add fractional class with user defined precision:

``` c++
inom::fractional<0.34, 9.44, 3> f = inom::make_fract<5.44>();
// or
inom::f<0.34, 9.44, 3> f = 5.44_fract;
```

The above represents a fractional value with 3 digits of precision between `0.340` and `9.440` of value `5.440`.
