Should not automatically prescribe the way TanhInterfaceSmoothing works

[jbisits]

Here I find the smoothing based off the initial conditions (which is good especially for single interface) but I prescribe the change over the interface as 100.0 (which is bad)

StaircaseShenanigans.jl/src/set_initial_conditions.jl

Lines 67 to 85 in cb83ac0

	function set_initial_conditions!(model, ics, interface_smoothing::Type{<:Tanh}, background_state)
	depth_of_interface = ics.depth_of_interface
	Lz = model.grid.Lz
	S = Array(ics.salinity_values)
	Sᵤ, Sₗ = S
	ΔS = diff(S)[1]
	S₀(x, y, z) = Tanh(Sₗ, ΔS, 100.0, depth_of_interface, abs(Lz))(x, y, z)
	T = Array(ics.temperature_values)
	Tᵤ, Tₗ = T
	ΔT = diff(T)[1]
	T₀(x, y, z) = Tanh(Tₗ, ΔT, 100.0, depth_of_interface, abs(Lz))(x, y, z)
	set!(model, S = S₀, T = T₀)
	return nothing
	end

Need to change this so user can add the steepness of the change.

[jbisits]

Closed with #104