Command consistency: suggestion

[Paul Jewell]

Good morning!

It struck me this weekend that there is some difference in the command 
structure for the different guix sub commands. For example:

guix package --list-generations

and

guix system list-generations

guix package has everything as an flag, but guix system (and guix home) 
uses the concept of ACTION with options and arguments.

Perhaps the latter is clearer, and guix package should also follow the 
same model?