refactor: unified input files handling

All commands's CLI was refactored to use new consistent handling of input files which allows selecting multiple input files as opposed to single archive/srcpkg:

input files as arguments:

apkg srcpkg -a foo.1.2.tgz foo.1.2.tgz.asc

input files listed in file(s) including stdin which allows piping:

apkg make-archive | apkg srcpkg -aF - | apkg build -sF -

Fixes: #30 (closed) Fixes: #31 (closed)