Use InverseFunctions.jl

[jlapeyre]

When I wrote this

LambertW.jl/src/LambertW.jl

Lines 199 to 207 in 76c8795

	# Example
	```julia-repl
	julia> import LambertW.finv
	julia> finv(lambertw)(lambertw(1))
	1.0
	```
	"""
	finv(::typeof(lambertw)) = W -> W * exp(W)

I suggested an interface for function inverses. Someone did this in InverseFunctions.jl.

We should add the two or three lines it takes to buy into this.