Support Vararg in @non_differentiable macro

[mzgubic]

Closes #212 .

[gxyd]

On top of your branch. When I do something like:

julia> @non_differentiable vcat(::Any, ::Vararg{AbstractArray{Int}})

it works just fine. But doing:

julia> @non_differentiable vcat(::Any, ::AbstractArray{Int}...)
syntax: "::AbstractArray{Int}" is not a valid function argument name

Stacktrace:
 [1] top-level scope at /Users/gaurav/.julia/packages/IJulia/a1SNk/src/kernel.jl:53

Is the second an incorrect Julia syntax?

[mzgubic]

Thanks for taking a look so quickly and catching this bug. What you showed is correct Julia syntax and should have been added.

[oxinabox]

This is great.
Some comments that you should adress before merging, but I don't think this will need further review