Setup header header struct.

[james-bird]

Very slow to construct/read into. I think it's to do with the use of static arrays, but haven't found a fix yet. Not yet tested the validity of data.

[stillyslalom]

Current header compilation time:

julia> t = time(); CineFiles.CineHeader("test/data/8bpp.cine"); time() - t
0.07999992370605469

After this PR:

julia> t = time(); CineFiles.CineHeader("test/data/8bpp.cine"); time() - t
46.08899998664856

Yeah, that's pretty painful. I think the main culprit is Description::SVector{4096,Char}, since compilation time drops to ~7.5 seconds if I comment that line out of the struct definition. Julia's compiler has issues with large tuples (JuliaLang/julia#35619), and the solution probably involves restructuring the setup header into a non-isbits type with Strings replacing each NTuple{N,Char}. I'll take a shot at it.

[james-bird]

The issue could be related to the issue discussed here:
https://discourse.julialang.org/t/long-parameter-for-type-seems-very-slow/63290

[james-bird]

I have made some changes which make the reading much more tolerable. The data looks sensible too, based on my limited testing.

[stillyslalom]

Looks mostly good - I've also considered iteratively reading the setup struct as a OrderedDict{Symbol,Any}, which might fractionally increase runtime, but would sharply decrease compilation time. That would also make it easier to handle the branches necessary to read older Setup header formats.