* alternatives: added parsing and setting of 'family' for an alternative
* alternatives: added checks for path nullability
* alternatives: added idempotence when setting alternative using family
* alternatives: added family to diff mode
* alternatives: added tests for family
* alternatives: updated documentation and examples
* alternatives: added constraints for 'path' and 'family' parameters.
in any invariants at least one of the parameters must be specified
* alternatives: added changelog fragment
* removed unnecessary check
* added version
Co-authored-by: Felix Fontein <felix@fontein.de>
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Co-authored-by: Felix Fontein <felix@fontein.de>