[WIP] Add the unsupported_file_type::Symbol kwarg to the Tar.create_tarball function

[DilumAluthge]

This pull request adds the unsupported_file_type::Symbol kwarg to the Tar.create_tarball function.

The possible values of unsupported_file_type are:

1. :error (default)
2. :warn

[DilumAluthge]

FYI, the motivation for the Options struct is that I was thinking we might add other similar options in the future, and it'll get real annoying to have to pass a lot of keyword arguments around everywhere, so I thought it would be easier to just pass around a single Options.

[StefanKarpinski]

The Options thing makes sense but should then probably include at least set_permissions and maybe some of the others.

[DilumAluthge]

Looks like this has gone pretty stale at this point.