Hi,

I tried creating a polynomial ratio:

```
using Polynomials
julia> a=Rational{Poly}(Poly([1,2]),Poly([3]))
```

, but got the following error:

```
ERROR: TypeError: Rational: in T, expected T<:Integer, got Type{Polynomials.Poly{T<:Number}}
```

It seems that the JuliaDSP group has crated a workaround, called the `PolynomialRatio`

:

```
DSP.Filters.PolynomialRatio{T<:Number}
```

Would it not be preferable to instead find a way to support `Poly`

directly from `Rational`

, given that polynomial ratios are not an uncommon occurance?