Replace `write_to_png` and `write_to_svg` by `write`

[mattuntergassmair]

I think the way we have currently solved this is not sufficient, as it allows syntax such as

c = render([roadway])
write("stadium.svg", c) # all good
write("stadium.png", c) # saves with .png suffix, but is actually an svg

We should really implement this in a way that the format of the file is deduced from the filename suffix (I think the plotting package does something very similar)

[MaximeBouton]

One of the challenge is that depending on the type of c we would not be able to save in any format, but I guess we could return an error message in that case.

• Any CairoSurface can be saved as .png
• For saving to svg or pdf it would need the correct surface type. If it is not the correct type, the write function could return an error message that tells how to fix it.

[MaximeBouton]

I will try to implement that soon, let's wait for this feature before merging #43

[mattuntergassmair]

Cool, sounds good. Yeah I'd say erroring is fine in that case and we can always leave write_to_svg etc. around and then just call that function from within Base.write() for convenience.

[MaximeBouton]

Distinguishing between svg and pdf is not trivial as CairoPDFSurface and CairoSVGSurface are actually of the same type (CairoSurfaceIOStream{UInt32}).

[MaximeBouton]

I think it should be solved in #43 now, related issue JuliaGraphics/Cairo.jl#316