Implement StarAlgebras

[blegat]

Currently, it gives

julia> @polyvar x
(x,)

julia> a = ChebyshevFirstKind(x)
Cheby1st(x)

julia> b = a * a
1//2·Cheby1st(x²) +1//2·Cheby1st(1)

julia> c = b * b
1//8·Cheby1st(x⁴) +1//8·Cheby1st(1) +1//8·Cheby1st(x²) +1//8·Cheby1st(x²) +1//8·Cheby1st(x²) +1//8·Cheby1st(x²) +1//8·Cheby1st(1) +1//8·Cheby1st(1)

[blegat]

https://www.jstor.org/stable/2002985

[blegat]

@kalmarek I'd like to do a quotient basis as well. Basically, you have a basis + a rewriting rule that you can use when you leave the basis (in my case it is Base.rem with a groebner basis as defined in SemialebraicSets), do you have something like that somewhere already ?