Summary:
Currently, archives offer three approaches.
1. `--archive` which takes an archive and puts all the output in a new
archive
2. No filename, which outputs based on the member names
3. Filename, which just matches everything.
This has a gap for when people wnat a single file without relying on
implicit naming that dumps all the contents to the CWD.
This PR adds `member` which lets you specify the member names as you
would get from `ar t libfoo.a` for this.