Add copy method for tikzdocument

[rs7q5]

Added a copy method for tikzdocument

closes PR #320.

[KristofferC]

Personally, I think all our deepcopys are wrong. For example, looking at how a container in Base behaves:

julia> d1 = Dict(1 => b)
Dict{Int64, Vector{Float64}} with 1 entry:
  1 => [0.908324, 0.17025, 0.383786]

julia> d2 = copy(d1)
Dict{Int64, Vector{Float64}} with 1 entry:
  1 => [0.908324, 0.17025, 0.383786]

julia> push!(b, 1)
4-element Vector{Float64}:
 0.9083239220321686
 0.1702504972071277
 0.38378559739161744
 1.0

julia> d2
Dict{Int64, Vector{Float64}} with 1 entry:
  1 => [0.908324, 0.17025, 0.383786, 1.0]

The copy here did not recursively copy each value in the dictionary. So this type of recursive copying done by deepcopy is unexpected for data that is provided by the user.

[tpapp]

So this type of recursive copying done by deepcopy is unexpected for data that is provided by the user.

I am not sure what the best solution would be then.

Maybe Base.copy could

1. copy options when applicable,

2. for types that have an elements or contents, copy those with copy.

I think this would be closest to the intended semantics of copy.

FWIW, I use PGFPlotsX exclusively for plotting, but have never had to copy anything. So maybe I am not the best person to decide this.

[KristofferC]

Yes, I would say you want to copy the options and the elements but not recursively copy "user values".

[rs7q5]

I will say this method did fix my error of there not being a base copy method for a function I was using that required a copy method. Granted the copy is more of a dummy copy I think. ... But yes, I usually copy the options.

Edit: should the method copy elements then but still output the td?