append + header about csv.jl HOT 1 CLOSED

julia> df
0×2 DataFrames.DataFrame

julia> names(df)
2-element Array{Symbol,1}:
 :col2
 :col3

julia> CSV.write("out.csv", df)
CSV.Sink{DateFormat{Symbol("yyyy-mm-dd"),Tuple{Base.Dates.DatePart{'y'},Base.Dates.Delim{Char,1},Base.Dates.DatePart{'m'},Base.Dates.Delim{Char,1},Base.Dates.DatePart{'d'}}},DataType}(    CSV.Options:
        delim: ','
        quotechar: '"'
        escapechar: '\\'
        null: ""
        dateformat: dateformat"yyyy-mm-dd"
        decimal: '.', IOBuffer(data=UInt8[...], readable=true, writable=true, seekable=true, append=false, size=0, maxsize=Inf, ptr=1, mark=-1), "out.csv", 10, true, String["col2", "col3"], 2, false, Val{false})

shell> cat out.csv
col2,col3