support for superancillaries via loading of EoSSuperancillaries.jl

[longemen3000]

superancillary support via pkg extensions. The workflow is the following:

1. load the package: using EoSSuperancillaries
2. that's it. the extension defined method for model::Union{SuperAncPCSAFT,SuperAncCubic} (hardcoded types that should support superancillaries.
3. the extension adds methods for x0_sat_pure, x0_crit_pure(model::SuperAncPCSAFT) and crit_pure(model::SuperAncPCSAFT). this is useful in the case of extended precision calculations where the results are not exactly the ancillary, while being a really good starting point.
4. the use of superancillaries can be turned on/off via Clapeyron.use_superancillaries!(val::Bool). This is useful for testing the default initial guess methods.