Write "clean" task

build.fsx

let appDirectory = Path.Combine("src", "PaketDemo")

let directoriesToClean () =
    DirectoryInfo.getSubDirectories (DirectoryInfo.ofPath "./src/")
    |> Array.collect (fun x -> [|Path.Combine(x.FullName, "bin"); Path.Combine(x.FullName, "obj")|])

Target.create "Clean" (fun _ ->
    Trace.log "--- Cleaning stuff ---"
    Shell.cleanDirs (directoriesToClean())
)