RFE: refactor to support rich command output

!175 (merged) brings new yaml input/output format which allows passing structured information between apkg commands as opposed to just a single file or a list of file as it is now.

Bring this functionality to all apkg commands to allow richer output and precise control while using same interface apkg commands use internally.

Also provide format only listing files for convenient shell scripting.

Showcase

> apkg make-archive

archive: pkg/archives/dev/knot-resolver-6.0.10.tar.xz
version: 6.0.10

> apkg get-archive

archive: pkg/archives/upstream/knot-resolver-6.0.10.tar.xz
archive_url: https://secure.nic.cz/files/knot-resolver/knot-resolver-6.0.10.tar.xz
signature: pkg/archives/upstream/knot-resolver-6.0.10.tar.xz.asc
signature_url: https://secure.nic.cz/files/knot-resolver/knot-resolver-6.0.10.tar.xz.asc
version: 6.0.10

srcpkg and build can describe the files they output, especially useful for Debian *_source.changes etc.

TODO

refactor all commands to:

• output YAML as opposed to just a list of files
• use new yaml format by default
• support current one-file-per-line format through --in-format list and --out-format list
• when passing files to commands, default to --in-format list to preserve current behavior
  • only support a single main file
• select input format with -f, --in-format
• select input output format with --out-format
  • find nice shortcut (-O is taken by --result-dir)