support xz package
fix sub-command detection
add `versions` command
add `--display-format` option
fix `--file` options completion
support [prev] section in setup.ini
add `upgrade` command
messages like the aptitude
refactoring
<pattern> matches orphan packages
command `versions` to display formatable
add `--download-only` option
change short options `-m` to `-M`, `-d` to `-m`
fix workspace detection
remove `--noscript` option
fix test statements
refactoring, if-then to one line