Allow setting mode for all Builder::append_* methods?

[iwinux]

Hi,

I'd like to control the mode / permission of files that are added to the archive, but it's very tedious to implement with current public APIs. Basically I need to copy all the append_* code from builder.rs to allow setting mode for append_dir_all and append_path_with_name.

It would be great if we can have something like append_dir_all_with_mode or something like that.