Add support for specialization on discretize

[Qfl3x]

If it's already implemented, please let me know. But looking at

PDEBase.jl/src/discretization_state.jl

Lines 55 to 90 in 9f71f68

	function SciMLBase.discretize(pdesys::PDESystem,
	discretization::AbstractEquationSystemDiscretization;
	analytic = nothing, kwargs...)
	sys, tspan = SciMLBase.symbolic_discretize(pdesys, discretization)
	try
	simpsys = structural_simplify(sys)
	if tspan === nothing
	add_metadata!(get_metadata(sys), sys)
	return prob = NonlinearProblem(simpsys, ones(length(simpsys.states));
	discretization.kwargs..., kwargs...)
	else
	# Use ODAE if nessesary
	if hasfield(typeof(sys.metadata), :use_ODAE) && sys.metadata.use_ODAE
	add_metadata!(get_metadata(simpsys),
	DAEProblem(simpsys; discretization.kwargs..., kwargs...))
	return prob = ODAEProblem(simpsys, Pair[], tspan; discretization.kwargs...,
	kwargs...)
	else
	add_metadata!(get_metadata(simpsys), sys)
	prob = ODEProblem(simpsys, Pair[], tspan; discretization.kwargs...,
	kwargs...)
	if analytic === nothing
	return prob
	else
	f = ODEFunction(pdesys, discretization, analytic = analytic,
	discretization.kwargs..., kwargs...)
	return ODEProblem(f, prob.u0, prob.tspan, prob.p;
	discretization.kwargs..., kwargs...)
	end
	end
	end
	catch e
	error_analysis(sys, e)
	end
	end

it doesn't appear to be implemented currently.