procedure LogFmt(const S: String; const Args: array of const);
Formats the string S using the series of arguments in the open array Args, and then logs it.
function OnDownloadProgress(const Url, FileName: String; const Progress, ProgressMax: Int64): Boolean;
begin
LogFmt('%s->%s: %d/%d', [Url, FileName, Progress, ProgressMax]);
Result := True;
end;