#965. Implemented MkStars.star() and MkStars.unstar() operations

See #986, release log:

• a47e766 by @null: Qulice remarks fixed
• b8da1aa by @null: PR remarks fixed
• 2653ff6 by @null: removed redundant @checkstyle
• 6772bd1 by @null: issue #965. Implemented MkStars.star() and MkStars.unstar() operations
• 6c261ad by @null: Merge remote branch 'fork/972'
• eaf5425 by @null: #972: simple variable names
• 364fcd5 by @null: Merge remote branch 'fork/963'
• 4caf30f by @null: #963 - incomplete documentation - review fix
• fc948e2 by @null: Merge remote branch 'fork/923'
• 0d2d4fc by @null: Updated according to Yegor's comments #2.
• 2673844 by @null: Updated according to Yegor's comments.
• 4a19636 by @null: #972: Stars no longer depends on user/repo parameters. It now has its own Repo, just like Hooks does.

Released by Rultor 1.47.1, see build log