Support Array Slicing

[lstagner]

I got bit by this yesterday. The solution is to write a custom getindex(A,I...) method but I am unsure about how to do that generically.

julia> x = Zeros(3,3)
3×3 Zeros{Float64,2,Tuple{Int64,Int64}}:
 0.0  0.0  0.0
 0.0  0.0  0.0
 0.0  0.0  0.0

julia> x[:,1]
3-element Array{Float64,1}:
 0.0
 0.0
 0.0

julia> x[1:3,1]
3-element Array{Float64,1}:
 0.0
 0.0
 0.0

[dlfivefifty]

See Tim Holy's comments in #26

Essentially one should step through every getindex implementation in Base and override it here. Probably ranges provide a blue print.

If you make a PR I'll gladly merge it.

[dlfivefifty]

This has been implemelented:

julia> x = Zeros(3,3)
3×3 Zeros{Float64}

julia> x[:,1]
3-element Zeros{Float64}

julia> x[1:3,1]
3-element Zeros{Float64}