Add constructor

We need points, and I bernstein ellipses are the way to go for intervals, which correspond to perturbed circles.    For circles, the following shows that radius*(1 - 1/n) is sufficient:

``` julia
n=86
    sc=[1/(1-1/n)^k for k=0:n-1]
    cfs=Fun(exp,Taylor((1-1/n)*𝕌),n).coefficients.*sc
    cfs-Fun(exp,Taylor(),n).coefficients|>norm  # always about eps()
```
