Save exchange volume data as a CSV file

[vnegi10]

Currently, exchange volume data is saved to a delimited (using ;) text file. Instead, we can save it as a CSV file. This will also reduce one dependency since DelimitedFiles.jl will no longer be needed.

In src/getdataCG.jl:

function get_vol_chart(exchange)
...

   open(filepath, "w") do f
        for chart in ex_vol_chart
            writedlm(f, [chart], ";")
        end
    end
...