Support JuMP.GenericModel

[DanielBrosch]

Right now PolyJuMP only seems to support Float64 Models:

using MultiFloats, JuMP, PolyJuMP, SumOfSquares
m = GenericModel{Float64x2}()
setpolymodule!(m, SumOfSquares)

Gives

ERROR: MethodError: no method matching setpolymodule!(::GenericModel{MultiFloat{Float64, 2}}, ::Module)

This package is quite convenient to use! But my instances are often numerically quite unstable, and require higher precision solvers.

[blegat]

It shouldn't be hard to do, we just need to replace Model by GenericModel at a few places